chore: update .repo-metadata.json (#655)

Author: parthea

.repo-metadata.json

@@ -4,13 +4,14 @@
     "product_documentation": "https://cloud.google.com/spanner/docs/",
     "client_documentation": "https://cloud.google.com/python/docs/reference/spanner/latest",
     "issue_tracker": "https://issuetracker.google.com/issues?q=componentid:190851%2B%20status:open",
-    "release_level": "ga",
+    "release_level": "stable",
     "language": "python",
     "library_type": "GAPIC_COMBO",
     "repo": "googleapis/python-spanner",
     "distribution_name": "google-cloud-spanner",
     "api_id": "spanner.googleapis.com",
     "requires_billing": true,
     "default_version": "v1",
-    "codeowner_team": "@googleapis/api-spanner-python"
+    "codeowner_team": "@googleapis/api-spanner-python",
+    "api_shortname": "spanner"
 }