mergify: backport-skip and backport-8.x are mutually exclusive (#14056)

.mergify.yml

@@ -176,15 +176,15 @@ pull_request_rules:
           * `backport-8./d` is the label to automatically backport to the `8./d` branch. `/d` is the digit.
           * `backport-8.x` is the label to automatically backport to the `8.x` branch.
 
-          **NOTE**: `backport-skip` has been added to this pull request.
-      label:
-        add:
-          - backport-skip
-  - name: add backport-8.x for the all the PRs targetting main
+  - name: add backport-8.x for the all the PRs targeting main if no skipped or assigned already
     conditions:
-      - -label~=^backport-\d
+      - -label~=^(backport-skip|backport-8.x)$
       - base=main
     actions:
+      comment:
+        message: |
+          `backport-8.x` has been added to help with the transition to the new branch `8.x`.
+          If you don't need it please use `backport-skip` label.
       label:
         add:
           - backport-8.x
@@ -195,6 +195,13 @@ pull_request_rules:
       label:
         remove:
           - backport-skip
+  - name: remove backport-8.x label if backport-skip is present
+    conditions:
+      - label~=^backport-skip
+    actions:
+      label:
+        remove:
+          - backport-8.x
   - name: notify the backport has not been merged yet
     conditions:
       - -merged