fix(git-extension): trim trailing whitespace before stripping commit-message quotes (#3673)

The auto-commit bash and Python twins strip a leading/trailing quote from
the configured `message:` value with an end-of-string-anchored quote strip.
When the YAML value has trailing whitespace after the closing quote
(`message: "Done"  `), the close-quote strip is anchored to end-of-string,
so it never matches the quote (spaces follow it). The commit message then
keeps a dangling quote and trailing spaces (`Done"  `).

The PowerShell twin already .Trim()s before stripping, so it produced the
clean `Done`. This left the three script variants out of parity. Trim the
value before stripping quotes in the bash and Python twins so all three
agree.

Verified at the exact-code level: the old bash sed pipeline yields
`spec done"  ` and the new one `spec done`; the Python _strip_quotes matches.
Add a parity regression test with trailing whitespace after the closing
quote (runs under CI where Git bash is resolvable).

extensions/git/scripts/python/auto_commit.py

@@ -33,7 +33,15 @@ def _value_after_colon(line: str) -> str:
 
 
 def _strip_quotes(value: str) -> str:
-    """Strip one leading quote and all trailing quotes, mirroring the bash sed."""
+    """Strip surrounding whitespace, then one leading quote and all trailing quotes.
+
+    Trimming first matters when the YAML value has trailing whitespace after a
+    closing quote (``message: "Done"  ``): stripping quotes anchored to the end
+    of string would leave the closing quote dangling (``Done"  ``) because the
+    quote is no longer at the end. The PowerShell twin ``.Trim()``s before
+    stripping, so trim here too to keep all three script variants in parity.
+    """
+    value = value.strip()
     value = re.sub(r"^[\"']", "", value)
     return re.sub(r"[\"']*$", "", value)