fix(renovate): correct file pattern for Jinja2 templates

Use managerFilePatterns with leading slash for proper regex matching

renovate.json

@@ -131,7 +131,7 @@
       "customType": "regex",
       "description": "Update Docker images in Jinja2 compose templates",
       "managerFilePatterns": [
-        "/^library/compose/.+/compose\\.ya?ml\\.j2$/"
+        "/library/compose/.+/compose\\.ya?ml\\.j2$/"
       ],
       "matchStrings": [
         "image:\\s*(?<depName>[^:\\s]+):(?<currentValue>[^\\s\\n{]+)"