Fix mergify batch merge issue (duplicated) (#3165)

@tensorflow/micro

Duplicate of #3164 for admin reasons.

Mergify recently added ability for batch merge, but that doesn't play well with our setup.
Setting max_parallel_check to 1 should resolve the issue and go back to how it was working before.

BUG=mergify fix

Co-authored-by: suleshahid <[email protected]>

Author: ddavis-2015

.github/mergify.yml

@@ -1,3 +1,6 @@
+merge_queue:
+  max_parallel_checks: 1
+
 queue_rules:
   - name: default
     checks_timeout: 2 h