chore(deps): bump actions/cache from 2.1.5 to 2.1.6

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](actions/cache@v2.1.5...v2.1.6)

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

Author: dependabot[bot]

.github/workflows/backend.yml

@@ -27,7 +27,7 @@ jobs:
         distribution: 'zulu'
         java-version: 16
 
-    - uses: actions/cache@v2.1.5
+    - uses: actions/cache@v2.1.6
       with:
         path: |
           ~/.gradle/caches
@@ -74,7 +74,7 @@ jobs:
           username: ${{ secrets.DOCKER_HUB_USERNAME }}
           password: ${{ secrets.DOCKER_HUB_PASSWORD }}
 
-      - uses: actions/cache@v2.1.5
+      - uses: actions/cache@v2.1.6
         with:
           path: |
             ~/.gradle/caches