Bump actions/cache from 4 to 5

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
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/main.yml

@@ -77,7 +77,7 @@ jobs:
       - name: CmdStan installation cacheing
         id: cache-cmdstan
         if: ${{ !startswith(needs.get-cmdstan-version.outputs.version, 'git:') }}
-        uses: actions/cache@v4
+        uses: actions/cache@v5
         with:
           path: ~/.cmdstan
           key: ${{ runner.os }}-cmdstan-${{ needs.get-cmdstan-version.outputs.version }}-${{ hashFiles('**/install_cmdstan.py') }}