chore: bump actions/cache from 3 to 4 (#78)

Bumps [actions/cache](https://github.com/actions/cache) from 3 to 4.
- [Release notes](https://github.com/actions/cache/releases)
- [Changelog](https://github.com/actions/cache/blob/main/RELEASES.md)
- [Commits](actions/cache@v3...v4)

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

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

.github/workflows/docs.yaml

@@ -26,7 +26,7 @@ jobs:
       - name: Run generate cache key
         run: echo "cache_id=$(date --utc '+%V')" >> $GITHUB_ENV
 
-      - uses: actions/cache@v3
+      - uses: actions/cache@v4
         with:
           key: mkdocs-cache-${{ env.cache_id }}
           path: .cache