Bump actions/cache from 4.1.2 to 4.2.0

Bumps [actions/cache](https://github.com/actions/cache) from 4.1.2 to 4.2.0.
- [Release notes](https://github.com/actions/cache/releases)
- [Changelog](https://github.com/actions/cache/blob/main/RELEASES.md)
- [Commits](actions/cache@6849a64...1bd1e32)

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

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

Author: dependabot[bot]

.github/workflows/app-tests.yaml

@@ -117,7 +117,7 @@ jobs:
             npm run build
 
         - name: Setup mypy cache
-          uses: actions/cache@6849a6489940f00c2f30c0fb92c6274307ccb58a # v4.1.2
+          uses: actions/cache@1bd1e32a3bdc45362d1e726936510720a7c30a57 # v4.2.0
           with:
             path: ./.mypy_cache
             key: mypy${{ matrix.os }}-${{ matrix.python_version }}-${{ hashFiles('requirements-dev.txt', 'src/backend/requirements.txt', 'src/backend/pyproject.toml') }}