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](https://github.com/actions/cache/compare/v3...v4)

---
updated-dependencies:
- dependency-name: actions/cache
  dependency-version: '4'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

.github/workflows/ci.yml

@@ -62,7 +62,7 @@ jobs:
           crystal: ${{ matrix.crystal }}
 
       - name: Cache Shards
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: |
             ./lib
@@ -141,7 +141,7 @@ jobs:
           crystal: latest
 
       - name: Cache Shards
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: |
             ./lib