docs/releasing: skip ci when creating the branchpoint

This isn't a new git state to be tested, we're just pushing it to a new location.

The push above doesn't need this because it doesn't run the CI anyway.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/39435>

docs/releasing.rst

@@ -211,7 +211,7 @@ the branches:
    git push origin $VERSION-branchpoint
    git checkout $VERSION-branchpoint
    git push origin HEAD:refs/heads/$VERSION
-   git push origin HEAD:refs/heads/staging/$VERSION
+   git push origin HEAD:refs/heads/staging/$VERSION --push-option ci.skip
    git checkout staging/$VERSION
    git branch --set-upstream-to origin/staging/$VERSION