Bump actions/cache from 3 to 4

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]>

Author: dependabot[bot]

.github/workflows/testsuite.yml

@@ -49,7 +49,7 @@ jobs:
 
     - name: Cache dependencies
       id: cache-dep
-      uses: actions/cache@v3
+      uses: actions/cache@v4
       with:
         path: ${{ steps.pip-cache.outputs.dir }}
         key: ${{ matrix.os }}-${{ matrix.python-version }}-pip-${{ hashFiles('**/requirements.txt') }}-${{ hashFiles('**/extra_requirements.txt') }}