fix: use --fixed-value flag when unsetting git config values

The tryConfigUnsetValue method was passing file paths directly to
`git config --unset`, which treats the value argument as an extended
regular expression. File paths contain `.` characters that would match
any character instead of literal periods, potentially causing incorrect
matches.

Adding the --fixed-value flag ensures the value is treated as a literal
string, fixing credential config cleanup in the v6-style authentication.

dist/index.js

@@ -979,7 +979,9 @@ class GitCommandManager {
             else {
                 args.push(globalConfig ? '--global' : '--local');
             }
-            args.push('--unset', configKey, configValue);
+            // Use --fixed-value to treat configValue as a literal string, not a regex pattern.
+            // This is important for file paths which contain regex special characters like '.'
+            args.push('--fixed-value', '--unset', configKey, configValue);
             const output = yield this.exec(args, { allowAllExitCodes: true });
             return output.exitCode === 0;
         });