build(deps): bump actions/cache from 4 to 5 (#22749)

Bumps [actions/cache](https://github.com/actions/cache) from 4 to 5.
- [Release notes](https://github.com/actions/cache/releases)
- [Changelog](https://github.com/actions/cache/blob/main/RELEASES.md)
- [Commits](actions/cache@v4...v5)

---
updated-dependencies:
- dependency-name: actions/cache
  dependency-version: '5'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/mill-plugin-tests.yaml

@@ -21,7 +21,7 @@ jobs:
           distribution: 'temurin'
       - name: Restore cache (read-only)
         # only use restore keys, no save key because we need to clear the cache before running the examples
-        uses: actions/cache/restore@v4
+        uses: actions/cache/restore@v5
         with:
           path: |
             ~/.m2/repository