Fix logic in lookup_blob to correctly return blob in bucket (#35475)

Co-authored-by: Nhon Dinh <nhon@dataxight.com>

Author: nhonx

sdks/python/apache_beam/io/gcp/gcsio_test.py

@@ -174,7 +174,8 @@ def lookup_blob(self, name):
     if name in bucket.blobs:
       return bucket.blobs[name]
     else:
-      return bucket.create_blob(name)
+      new_blob = bucket._create_blob(name)
+      return bucket.add_blob(new_blob)
 
   def set_default_kms_key_name(self, name):
     self.default_kms_key_name = name