Bump scientific-python/attach-next-milestone-action (#30)

Bumps [scientific-python/attach-next-milestone-action](https://github.com/scientific-python/attach-next-milestone-action) from f94a5235518d4d34911c41e19d780b8e79d42238 to a4889cfde7d2578c1bc7400480d93910d2dd34f6.
- [Release notes](https://github.com/scientific-python/attach-next-milestone-action/releases)
- [Commits](scientific-python/attach-next-milestone-action@f94a523...a4889cf)

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

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.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@f94a5235518d4d34911c41e19d780b8e79d42238
+      - uses: scientific-python/attach-next-milestone-action@a4889cfde7d2578c1bc7400480d93910d2dd34f6
         with:
           token: ${{ secrets.MILESTONE_LABELER_TOKEN }}
           force: true