build(deps): bump actions/cache from 2.1.5 to 2.1.6 (#23983)

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/linux_build_tests.yaml

@@ -49,7 +49,7 @@ jobs:
         - ruby-rake  # RubyPackage
     steps:
     - uses: actions/checkout@v2
-    - uses: actions/cache@v2.1.5
+    - uses: actions/cache@v2.1.6
       with:
         path: ~/.ccache
         key: ccache-build-${{ matrix.package }}