make validation for BQ export source configurable (#34651)

Author: elzino

Diff for: sdks/python/apache_beam/io/gcp/bigquery.py

@@ -784,14 +784,15 @@ def _get_project(self):
 
   def _create_source(self, path, coder):
     if not self.use_json_exports:
-      return create_avro_source(path)
+      return create_avro_source(path, validate=self.validate)
     else:
       return TextSource(
           path,
           min_bundle_size=0,
           compression_type=CompressionTypes.UNCOMPRESSED,
           strip_trailing_newlines=True,
-          coder=coder)
+          coder=coder,
+          validate=self.validate)
 
   def split(self, desired_bundle_size, start_position=None, stop_position=None):
     if self.export_result is None: