ci(mergify): upgrade configuration to current format

Author: mergify[bot]

.github/mergify.yml

@@ -54,7 +54,7 @@ pull_request_rules:
       - "#assignee=0"
     actions:
       assign:
-        users: [ "rohenaz" ]
+        users: ["rohenaz"]
 
   # ===============================================================================
   # ALERTS
@@ -165,10 +165,10 @@ pull_request_rules:
   - name: Welcome New Contributors
     conditions:
       - and:
-        - author!=dependabot[bot]
-        - author!=mergify[bot]
-        - author!=rohenaz
-        - author!=rohenaz
+          - author!=dependabot[bot]
+          - author!=mergify[bot]
+          - author!=rohenaz
+          - author!=rohenaz
     actions:
       comment:
         message: |
@@ -188,17 +188,7 @@ 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
@@ -220,4 +210,4 @@ 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 %}