Fix mergify configuration

With the fix of code owners, we removed the top level reviewers
group. This enabled us to align with the purpose of codeowners
file.

After the fix merged, the mergify configuration was left unchanged
resulting in a broken condition.

This PR fixes the mergify conditions and moves the merge mechanism
to queue.

Signed-off-by: Pragadeeswaran Sathyanarayanan <pragadeeswaran.sathyanarayanan@ibm.com>
Signed-off-by: Harishacharya-redhat <hacharya@redhat.com>

Author: psathyan

.github/mergify.yml

@@ -5,12 +5,12 @@ pull_request_rules:
       - label!=DNM
       - label!=work-in-progress
       - base=main
-      - "approved-reviews-by=@red-hat-storage/cephci-top-level-reviewers"
+      - branch-protection-review-decision=approved
       - "check-success=tox (3.9.18)"
       - check-success=WIP
     actions:
-      merge:
-        method: merge
+      queue:
+        merge_method: merge
   - name: ask to resolve conflict
     conditions:
       - conflict