fix lint

Author: GarrettBeatty

.doc_gen/metadata/s3_metadata.yaml

@@ -3719,7 +3719,7 @@ s3_CreatePresignedPost:
         - sdk_version: 4
           github: dotnetv4/S3
           excerpts:
-            - description: Create a presigned POST URL
+            - description: Create a presigned POST URL.
               genai: most
               snippet_tags:
                 - S3.dotnetv4.Scenario_CreatePresignedPostAsync