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/bash/auto-commit.sh

@@ -94,7 +94,12 @@ if [ -f "$_config_file" ]; then
                     [ "$_val" = "false" ] && _enabled=false
                 fi
                 if echo "$_line" | grep -Eq '[[:space:]]+message:'; then
-                    _commit_msg=$(echo "$_line" | sed 's/^[^:]*:[[:space:]]*//' | sed 's/^["'\'']//' | sed 's/["'\'']*$//')
+                    # Trim trailing whitespace before stripping the closing quote:
+                    # a value like `message: "Done"  ` (trailing spaces after the
+                    # quote) would otherwise leave the quote dangling (`Done"  `),
+                    # since the closing-quote strip is anchored to end-of-string.
+                    # The PowerShell twin .Trim()s first; match it for parity.
+                    _commit_msg=$(echo "$_line" | sed 's/^[^:]*:[[:space:]]*//' | sed 's/[[:space:]]*$//' | sed 's/^["'\'']//' | sed 's/["'\'']*$//')
                 fi
             fi
         fi