mergify: avoid label automation always (#3892)

Force merging as tests won't pass before a 9.x release is available.

.mergify.yml

@@ -264,16 +264,17 @@ pull_request_rules:
           To fixup this pull request, you need to add the backport labels for the needed
           branches, such as:
           * `backport-./d./d` is the label to automatically backport to the `8./d` branch. `/d` is the digit
-  - name: add backport-8.x label for main only
+  - name: add backport-8.x label for main only if no skipped or assigned already
     conditions:
-      - -label~=^backport-8.x
+      - -label~=^(backport-skip|backport-8.x)$
       - base=main
       - -merged
       - -closed
     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 and remove the `backport-8.x` label.
       label:
         add:
           - backport-8.x