Bump actions/cache from 3 to 4 (#327)

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/documenter.yml

@@ -22,7 +22,7 @@ jobs:
       - uses: julia-actions/cache@v1
       - name: Cache CondaPkg
         id: cache-condaPkg
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         env:
           cache-name: cache-condapkg
         with:
@@ -32,7 +32,7 @@ jobs:
             ${{ runner.os }}-${{ env.cache-name }}-
       - name: Cache CmdStan
         id: cache-cmdstan
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: ${{ env.CMDSTAN_PATH }}
           key: cmdstan-${{ env.CMDSTAN_VERSION }}-${{ runner.os }}