ci(mergify): upgrade configuration to current format

Author: mergify[bot]

.github/mergify.yml

@@ -8,7 +8,7 @@ pull_request_rules:
     conditions:
       - -draft
       - author~=^dependabot(|-preview)\[bot\]$
-      - check-success='test (1.24.x, ubuntu-latest)' 
+      - check-success='test (1.24.x, ubuntu-latest)'
       - title~=^Bump [^\s]+ from ([\d]+)\..+ to \1\.
     actions:
       review:
@@ -163,11 +163,11 @@ pull_request_rules:
   - name: Welcome New Contributors
     conditions:
       - and:
-        - author!=dependabot[bot]
-        - author!=mergify[bot]
-        - author!=rohenaz
-        - author!=rohenaz
-        - author!=icellan
+          - author!=dependabot[bot]
+          - author!=mergify[bot]
+          - author!=rohenaz
+          - author!=rohenaz
+          - author!=icellan
     actions:
       comment:
         message: Welcome to our open-source project! 💘
@@ -186,17 +186,7 @@ pull_request_rules:
         message: |
           This pull request looks stale. Feel free to reopen it if you think it's a mistake.
       label:
-        add: [ "stale" ]
-
-  # ===============================================================================
-  # BRANCHES
-  # ===============================================================================
-
-  - name: Delete head branch after merge
-    conditions:
-      - merged
-    actions:
-      delete_head_branch:
+        add: ["stale"]
 
   # ===============================================================================
   # CONVENTION
@@ -218,4 +208,4 @@ pull_request_rules:
   #      summary: |
   #        {% if not check_succeed %}
   #        Your pull request title must follow [Conventional Commit](https://www.conventionalcommits.org/en/v1.0.0/).
-  #        {% endif %}
+  #        {% endif %}