feat(github actions): discover workflow files in subfolders (#13143)

lib/manager/github-actions/index.ts

@@ -4,7 +4,7 @@ export { extractPackageFile };
 
 export const defaultConfig = {
   fileMatch: [
-    '^(workflow-templates|\\.github\\/workflows)\\/[^/]+\\.ya?ml$',
+    '(^workflow-templates|\\.github\\/workflows)\\/[^/]+\\.ya?ml$',
     '(^|\\/)action\\.ya?ml$',
   ],
 };