Published the coverage report instead of everything the run produced (#655)

The download step in deploy_code_coverage asked for the artifact named
${{ steps.artifact.outputs.coverage_report }}. That output is set by the
"Coverage Report name" step of run_tests, which is a different job, and the
steps context does not cross jobs. So the expression evaluated to the empty
string and the action took its documented path for an unspecified name:

    No input name, artifact-ids or pattern filtered specified,
    downloading all artifacts
    Total of 4 artifact(s) downloaded

The four are the two coverage reports and the two test_reports bundles of
JUnit XML, each extracted into a directory named after the artifact. The
next step uploads the lot to Pages, so the published site has carried the
test reports alongside the coverage, one directory deeper than intended,
under a path containing a run timestamp that changed on every publish. Any
link to a coverage report broke the next time one was published.

Selecting by pattern with merge-multiple fixes both halves: the pattern
excludes the test_reports bundles, and merging puts the contents of the two
coverage artifacts directly into coverage_report rather than under a
directory named for each. Each artifact holds one directory named for its
suite, renamed from default_build_coverage by "Prepare Coverage GitHub
Pages", so the result is the two suite directories the deploy expects and
the timestamped artifact name no longer appears in the published path.

Verified on a runner rather than reasoned about, with an isolated workflow
that uploads artifacts shaped like the real ones and downloads them both
ways:

    OLD  coverage_report/coverage_report-<epoch>-ThreadX/ThreadX/index.html
         coverage_report/coverage_report-<epoch>-ThreadX/default_build_coverage.xml
         coverage_report/coverage_report-<epoch>-SMP/SMP/index.html
         coverage_report/coverage_report-<epoch>-SMP/default_build_coverage.xml
         coverage_report/test_reports SMP/results.xml
         coverage_report/test_reports ThreadX/results.xml

    NEW  coverage_report/ThreadX/index.html
         coverage_report/SMP/index.html
         coverage_report/default_build_coverage.xml

Both artifacts carry a default_build_coverage.xml and the merge means one
overwrites the other, which the run above also shows. That file is consumed
by CodeCoverageSummary back in run_tests and is not read here, so it is
untidy rather than wrong, and it is called out in a comment.

The delete step is fixed in the same place and for a related reason. The
artifacts are named coverage_report-<epoch>, useGlob defaults to true in
this action, and as a glob "coverage_report" matches only the literal
string. It has been deleting nothing, without failing, and retention-days: 1
on the upload is what has actually been clearing these up.

Assisted-by: Claude Opus 5 <noreply@anthropic.com>

.github/workflows/regression_template.yml

@@ -178,10 +178,37 @@ jobs:
       id-token: write
 
     steps:
+    # Selects the coverage artifacts by pattern rather than by name.
+    #
+    # This used to ask for ${{ steps.artifact.outputs.coverage_report }},
+    # which is set by the "Coverage Report name" step of run_tests -- a
+    # different job. The steps context does not cross jobs, so that
+    # expression evaluated to the empty string and the action fell back to
+    # its documented behaviour for an unspecified name: "No input name,
+    # artifact-ids or pattern filtered specified, downloading all
+    # artifacts". It pulled down four, the two coverage reports and the two
+    # test_reports bundles of JUnit XML, each into a directory named after
+    # the artifact -- so the published site carried the test reports as well
+    # as the coverage, under paths containing a run timestamp that changed
+    # on every publish.
+    #
+    # merge-multiple puts the contents of both coverage artifacts directly
+    # into coverage_report rather than under a directory named for each
+    # artifact. Each one holds a single directory named for its suite,
+    # ThreadX or SMP, renamed from default_build_coverage by the "Prepare
+    # Coverage GitHub Pages" step, so the merge yields exactly the two
+    # suite directories the deploy expects, and the artifact name -- with
+    # its timestamp -- stops appearing in the published path at all.
+    #
+    # The two artifacts also each carry a default_build_coverage.xml, and
+    # the merge means one overwrites the other. That file is consumed by
+    # CodeCoverageSummary back in run_tests and is not read here, so this is
+    # untidy rather than wrong.
     - uses: actions/download-artifact@v4.3.0
       if: ${{ inputs.skip_test }}
       with:
-        name: ${{ steps.artifact.outputs.coverage_report }}
+        pattern: coverage_report-*
+        merge-multiple: true
         path: ${{ inputs.cmake_path }}/coverage_report
 
     - name: Upload Code Coverage Pages
@@ -190,10 +217,16 @@ jobs:
       with:
         path: .
 
+    # The artifacts are named coverage_report-<epoch> by run_tests, so the
+    # bare name matched nothing: useGlob defaults to true in this action, and
+    # as a glob "coverage_report" matches only the literal string. The step
+    # has therefore been deleting nothing. It does not fail on a miss, which
+    # is why that went unnoticed; retention-days: 1 on the upload is what has
+    # actually been clearing these up.
     - name: Delete Duplicate Code Coverage Artifact
       uses: geekyeggo/delete-artifact@v5.1.0
       with:
-          name: coverage_report
+          name: coverage_report-*
 
     - name: Deploy GitHub Pages site
       id: deployment