ci(dev_container): drop branch push trigger on release branches

Pushes to stable/beta/release/** only move when a release is cut, and
that release was already built by the matching v* tag push moments
earlier. The subsequent branch push reruns the arm64+amd64 matrix
(~8 min) to produce the identical image digest. Registry push is
already gated on refs/tags/, so the second run is pure waste.

Drop those branches from on.push; keep main (regular development
pushes) and the v* tag trigger (the authoritative release trigger).
workflow_dispatch remains available for manual rebuilds.

Fixes #27170

Signed-off-by: Ramon Roche <mrpollo@gmail.com>

.github/workflows/dev_container.yml

@@ -4,9 +4,6 @@ on:
   push:
     branches:
       - 'main'
-      - 'stable'
-      - 'beta'
-      - 'release/**'
     tags:
       - 'v*'
   pull_request: