fix: return 403 when VPC-SC violation happens (googleapis#1131)

This is fixing the issue where VPC-SC violation is not returning 403. Error message map does not recognize VPCSC policy violation error and will default to return an internal server error.

Co-authored-by: Tim Swast <swast@google.com>

google/cloud/bigquery/job/base.py

@@ -45,6 +45,7 @@
     "invalidQuery": http.client.BAD_REQUEST,
     "notFound": http.client.NOT_FOUND,
     "notImplemented": http.client.NOT_IMPLEMENTED,
+    "policyViolation": http.client.FORBIDDEN,
     "quotaExceeded": http.client.FORBIDDEN,
     "rateLimitExceeded": http.client.FORBIDDEN,
     "resourceInUse": http.client.BAD_REQUEST,