samples: update synth.py to exclude samples.yaml (#536)

Author: anguillanneuf

java-pubsub/synth.py

@@ -522,4 +522,6 @@
     java.format_code(f'grpc-google-cloud-{service}-{version}/src')
     java.format_code(f'proto-google-cloud-{service}-{version}/src')
 
-java.common_templates()
+java.common_templates(excludes=[
+  ".github/workflows/samples.yaml",
+])