Bump actions/cache from 2 to 4 (#77)

Bumps [actions/cache](https://github.com/actions/cache) from 2 to 4.
- [Release notes](https://github.com/actions/cache/releases)
- [Changelog](https://github.com/actions/cache/blob/main/RELEASES.md)
- [Commits](actions/cache@v2...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/ci.yml

@@ -34,7 +34,7 @@ jobs:
  submodules: true
 
  - name: Reuse ccache directory
- uses: actions/cache@v2
+ uses: actions/cache@v4
  with:
  path: ~/.ccache
  key: '${{matrix.os}} ${{matrix.info}} ccache-dir ${{github.ref}} run-${{github.run_number}}'

.github/workflows/docker.yaml

@@ -19,7 +19,7 @@ jobs:
  submodules: true
 
  - name: Reuse ccache directory
- uses: actions/cache@v2
+ uses: actions/cache@v4
  with:
  path: .ccache
  key: 'ccache-dir-${{github.ref}}_run-${{github.run_number}}'