add gcs-spanner-dv path to spanner-pr.yaml workflow (#3455)

Author: derrickaw

.github/workflows/spanner-pr.yml

@@ -35,6 +35,7 @@ on:
       - '.github/workflows/spanner-pr.yml'
       - 'v2/datastream-to-spanner/**'
       - 'v2/spanner-change-streams-to-sharded-file-sink/**'
+      - 'v2/gcs-spanner-dv/**'
       - 'v2/gcs-to-sourcedb/**'
       - 'v2/sourcedb-to-spanner/**'
       - 'v2/spanner-to-sourcedb/**'