build(deps): Bump actions/cache from 2.1.6 to 2.1.7

Bumps [actions/cache](https://github.com/actions/cache) from 2.1.6 to 2.1.7.
- [Release notes](https://github.com/actions/cache/releases)
- [Commits](https://github.com/actions/cache/compare/v2.1.6...v2.1.7)

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

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

.github/workflows/tests.yaml

@@ -60,7 +60,7 @@ jobs:
         echo "::set-output name=dir::$(pip cache dir)"
     - name: set pip cache
       id: pip-cache
-      uses: actions/[email protected].6
+      uses: actions/[email protected].7
       with:
         path: ${{ steps.pip-cache-dir.outputs.dir }}
         key: ${{ runner.os }}-pip-${{ hashFiles('setup.cfg') }}