github: Fix a mergify error

Mergify won't merge changes due to the following error:

"The branch protection setting Require branches to be up to date
beforemerging is not compatible with max_parallel_checks>1,
queue_conditions != merge_conditions and must be unset."

Signed-off-by: Anoop C S <[email protected]>

Author: anoopcs9

.github/mergify.yml

@@ -127,3 +127,6 @@ pull_request_rules:
       label:
         add:
           - "priority-review"
+
+merge_queue:
+  max_parallel_checks: 1