Bump actions/cache from 2 to 4

Bumps [actions/cache](https://github.com/actions/cache) from 2 to 4.
- [Release notes](https://github.com/actions/cache/releases)
- [Changelog](https://github.com/actions/cache/blob/main/RELEASES.md)
- [Commits](https://github.com/actions/cache/compare/v2...v4)

---
updated-dependencies:
- dependency-name: actions/cache
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

.github/workflows/coverage.yml

@@ -20,7 +20,7 @@ jobs:
         uses: actions/checkout@v2
 
       - name: Cache go module
-        uses: actions/cache@v2
+        uses: actions/cache@v4
         id: cache-gomodules
         with:
           path: ~/go/pkg/mod

.github/workflows/test.yml

@@ -32,7 +32,7 @@ jobs:
         uses: actions/checkout@v2
 
       - name: Cache go module
-        uses: actions/cache@v2
+        uses: actions/cache@v4
         with:
           path: ~/go/pkg/mod
           key: ${{ runner.os }}-go-${{ hashFiles('**/go.sum') }}