Bump actions/cache from 3 to 4 (#30)

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] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/ci_testing.yml

@@ -49,7 +49,7 @@ jobs:
       run: echo "dir=$(pip cache dir)" >> $GITHUB_OUTPUT
 
     - name: Cache pip
-      uses: actions/cache@v3
+      uses: actions/cache@v4
       with:
         path: ${{ steps.pip-cache.outputs.dir }}
         key: ${{ runner.os }}-${{ matrix.python-version }}-pip-${{ hashFiles('requirements.txt') }}

.github/workflows/code-format.yml

@@ -23,7 +23,7 @@ jobs:
 
       - name: set PY
         run: echo "PY=$(python -VV | sha256sum | cut -d' ' -f1)" >> $GITHUB_ENV
-      - uses: actions/cache@v3
+      - uses: actions/cache@v4
         with:
           path: ~/.cache/pre-commit
           key: pre-commit|${{ env.PY }}|${{ hashFiles('.pre-commit-config.yaml') }}