chore: preserve ConnectionProto.java (#453)

Author: Neenu1995

.github/.OwlBot.yaml

@@ -23,6 +23,7 @@ deep-remove-regex:
 deep-preserve-regex:
 - "/google-cloud-bigqueryconnection/src/test/java/com/google/cloud/bigqueryconnection/v.*/it/ITSystemTest.java"
 - "/proto-google-cloud-bigqueryconnection-v1/src/main/java/com/google/cloud/bigquery/connection/v1/ConnectionProto.java"
+- "/proto-google-cloud-bigqueryconnection-v1/src/main/java/com/google/cloud/bigquery/connection/ConnectionProto.java"
 
 deep-copy-regex:
 - source: "/google/cloud/bigquery/connection/(v.*)/.*-java/proto-google-.*/src"