chore: update release_level in repo-metadata.json (#326)

* chore: update .repo-metadata.json

* revert

* remove api_shortname

Author: parthea

packages/google-api-core/.repo-metadata.json

@@ -2,7 +2,7 @@
     "name": "google-api-core",
     "name_pretty": "Google API client core library",
     "client_documentation": "https://googleapis.dev/python/google-api-core/latest",
-    "release_level": "ga",
+    "release_level": "stable",
     "language": "python",
     "library_type": "CORE",
     "repo": "googleapis/python-api-core",