build(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](https://github.com/actions/cache/compare/v2.1.5...v2.1.6)

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

.github/workflows/linux-workflow.yml

@@ -85,7 +85,7 @@ jobs:
           message("::set-output name=timestamp::${current_date}")
 
       - name: ccache cache files
-        uses: actions/[email protected].5
+        uses: actions/[email protected].6
         with:
           path: .ccache
           key: ${{ matrix.os }}-${{ matrix.platform }}-${{ matrix.compiler }}${{ matrix.detail }}-ccache-${{ steps.ccache_cache_timestamp.outputs.timestamp }}