github-actions: bump actions/cache from v2 to v2.1.4

Bumps [actions/cache](https://github.com/actions/cache) from v2 to v2.1.4.
- [Release notes](https://github.com/actions/cache/releases)
- [Commits](actions/cache@v2...26968a0)

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

Author: dependabot[bot]

.github/workflows/changelog.yml

@@ -20,7 +20,7 @@ jobs:
         uses: ruby/setup-ruby@v1
         with:
           ruby-version: 3.0
-      - uses: actions/cache@v2
+      - uses: actions/cache@v2.1.4
         with:
           path: vendor/bundle
           key: ${{ runner.os }}-changelog-gem