revert firestore version in state.yaml

Author: noahdietz

.librarian/state.yaml

@@ -2693,7 +2693,7 @@ libraries:
       - packages/google-cloud-financialservices/docs/
     tag_format: '{id}-v{version}'
   - id: google-cloud-firestore
-    version: 2.28.0
+    version: 2.27.0
     last_generated_commit: a78b5838b801428bfe5b85758727a46d830b7f39
     apis:
       - path: google/firestore/admin/v1