Bump scientific-python/attach-next-milestone-action in the actions group

Bumps the actions group with 1 update: [scientific-python/attach-next-milestone-action](https://github.com/scientific-python/attach-next-milestone-action).


Updates `scientific-python/attach-next-milestone-action` from bc07be829f693829263e57d5e8489f4e57d3d420 to c9cfab10ad0c67fed91b01103db26b7f16634639
- [Release notes](https://github.com/scientific-python/attach-next-milestone-action/releases)
- [Commits](scientific-python/attach-next-milestone-action@bc07be8...c9cfab1)

---
updated-dependencies:
- dependency-name: scientific-python/attach-next-milestone-action
  dependency-type: direct:production
  dependency-group: actions
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/milestone-merged-prs.yaml

@@ -12,7 +12,7 @@ jobs:
     name: attach to PR
     runs-on: ubuntu-latest
     steps:
-      - uses: scientific-python/attach-next-milestone-action@bc07be829f693829263e57d5e8489f4e57d3d420
+      - uses: scientific-python/attach-next-milestone-action@c9cfab10ad0c67fed91b01103db26b7f16634639
         with:
           token: ${{ secrets.MILESTONE_LABELER_TOKEN }}
           force: true