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](https://github.com/actions/cache/compare/v3...v4)

---
updated-dependencies:
- dependency-name: actions/cache
  dependency-version: '4'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/comprehensive_tests.yml

@@ -41,7 +41,7 @@ jobs:
     # Step 4: Cache dependencies to speed up subsequent runs.
     - name: Load cached venv
       id: cached-poetry-dependencies
-      uses: actions/cache@v3
+      uses: actions/cache@v4
       with:
         path: .venv
         key: venv-${{ runner.os }}-${{ steps.setup-python.outputs.python-version }}-${{ hashFiles('**/poetry.lock') }}