Revert "backport.yml: use a PAT token of a user with write access to …

…the repo"

This reverts commit 64971a1.

.github/workflows/backport.yml

@@ -22,4 +22,4 @@ jobs:
         if: github.event.pull_request.merged && ( ( github.event.action == 'closed' && contains( join( github.event.pull_request.labels.*.name ), 'backport') ) || contains( github.event.label.name, 'backport' ) )
         uses: m-kuhn/backport@v1.2.7
         with:
-          github_token: ${{ secrets.MAPSERVER_ROUAULT_BACKPORT_TOKEN }}
+          github_token: ${{ secrets.GITHUB_TOKEN }}