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] <support@github.com>

Author: dependabot[bot]

.github/workflows/build.yml

@@ -52,7 +52,7 @@ jobs:
       - run: sudo apt-get update
       - name: Restore opam cache
         id: opam-cache
-        uses: actions/cache@v4
+        uses: actions/cache@v5
         with:
           path: ${{github.workspace}}/_opam
           key: opam-${{env.OCAML_COMILER_VERSION}}-${{hashFiles('.github/coq-concert.opam.locked')}}

.github/workflows/refresh-cache.yml

@@ -21,7 +21,7 @@ jobs:
       - run: sudo apt-get update
       - name: Restore opam cache
         id: opam-cache
-        uses: actions/cache@v4
+        uses: actions/cache@v5
         with:
           path: ${{github.workspace}}/_opam
           fail-on-cache-miss: true