Replace em dash inside YAML test payload with hyphen

Windows CI runners write to disk with the system default encoding
(CP-1252 on en-US). An em dash inside the YAML written via
``Path.write_text`` lands as byte 0x97, which then trips
``read_text(encoding='utf-8')`` later in command_rename. Em dashes
in Python source / comments are fine -- the interpreter reads
source as UTF-8 by default -- the only constraint is for content
that round-trips through write_text + read_text(utf-8).

tests/unit_tests/test_main.py

@@ -3688,7 +3688,7 @@ esphome:
   name: ${device_name}
 
 # A copy-pasted block that re-declares the substitution at the
-# same indent level — happens when users splice in a packaged
+# same indent level - happens when users splice in a packaged
 # fragment without renaming the variable.
 example:
   device_name: oldname