Bump actions/cache from v1.2.0 to v2

Bumps [actions/cache](https://github.com/actions/cache) from v1.2.0 to v2.
- [Release notes](https://github.com/actions/cache/releases)
- [Commits](actions/cache@v1.2.0...b820478)

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

Author: dependabot[bot]

.github/workflows/tests.yml

@@ -65,7 +65,7 @@ jobs:
           print("::set-output name=result::{}".format(result))
 
       - name: Restore pre-commit cache
-        uses: actions/cache@v1.2.0
+        uses: actions/cache@v2
         if: matrix.session == 'pre-commit'
         with:
           path: ~/.cache/pre-commit