Bump actions/cache from 2.1.5 to 2.1.6 (#2830)

Bumps [actions/cache](https://github.com/actions/cache) from 2.1.5 to 2.1.6.
- [Release notes](https://github.com/actions/cache/releases)
- [Commits](https://github.com/actions/cache/compare/v2.1.5...v2.1.6)

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

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

.github/workflows/test.yml

@@ -19,7 +19,7 @@ jobs:
 
       - name: Cache Qt
         id: cache-qt
-        uses: actions/cache@v2.1.5
+        uses: actions/cache@v2.1.6
         with:
           path: ../Qt
           key: ${{ runner.os }}-QtCache-20201005