Bump actions/cache from 2.1.4 to 2.1.6

Bumps [actions/cache](https://github.com/actions/cache) from 2.1.4 to 2.1.6.
- [Release notes](https://github.com/actions/cache/releases)
- [Commits](actions/cache@v2.1.4...v2.1.6)

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

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -23,7 +23,7 @@ jobs:
                 jdk: [11, 15, 16]
         steps:
             - uses: actions/checkout@v2
-            - uses: actions/[email protected].4
+            - uses: actions/[email protected].6
               with:
                 path: |
                     ~/.gradle/caches
@@ -53,7 +53,7 @@ jobs:
               with:
                   fetch-depth: '0' # https://github.com/shipkit/shipkit-changelog#fetch-depth-on-ci
 
-            - uses: actions/[email protected].4
+            - uses: actions/[email protected].6
               with:
                 path: |
                   ~/.gradle/caches