Bump actions/cache from 3 to 4 (#4873)

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

.github/workflows/docs.yml

@@ -15,7 +15,7 @@ jobs:
           repository: JuliaPlots/PlotDocs.jl
       - uses: julia-actions/setup-julia@latest
       - name: Cache artifacts
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         env:
           cache-name: cache-artifacts
         with: