Bump actions/cache from 3 to 6

Bumps [actions/cache](https://github.com/actions/cache) from 3 to 6.
- [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...v6)

---
updated-dependencies:
- dependency-name: actions/cache
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

.github/workflows/python-ci.yml

@@ -70,7 +70,7 @@ jobs:
         shell: bash
         run: echo "${{ steps.msys.outputs.msys2-location }}/mingw64/bin" >> $GITHUB_PATH
       - name: Cache pip
-        uses: actions/cache@v3
+        uses: actions/cache@v6
         with:
           path: ~/.cache/pip
           key: ${{ runner.os }}-pip-${{ hashFiles('requirements.lock') }}