GH Actions: Bump actions/cache from 3 to 4

Bumps [actions/cache](https://github.com/actions/cache) from 3 to 4.
- [Release notes](https://github.com/actions/cache/releases)
- [Changelog](https://github.com/actions/cache/blob/main/RELEASES.md)
- [Commits](actions/cache@v3...v4)

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

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

.github/workflows/update-cacert.yml

@@ -58,7 +58,7 @@ jobs:
         uses: actions/checkout@v4
 
       - name: Restore etags cache for certificate files
-        uses: actions/cache@v2
+        uses: actions/cache@v4
         with:
           path: certificates/etag-*.txt
           key: curl-etag-${{ hashFiles('certificates/cacert.pem') }}-${{ hashFiles('certificates/cacert.pem.sha256') }}