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/ci.yml

@@ -57,7 +57,7 @@ jobs:
       uses: actions/checkout@v4
     - name: 'Cache Maven repo'
       if: ${{ !(matrix.experimental && github.event_name == 'pull_request') }}
-      uses: actions/cache@v3
+      uses: actions/cache@v4
       with:
           path: |
             ~/.m2/repository

.github/workflows/pitest.yml

@@ -25,7 +25,7 @@ jobs:
           fetch-depth: 2
 
       - name: Cache Maven repository
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: ~/.m2/repository
           key: ${{ runner.os }}-mvn-pitest-${{ hashFiles('**/pom.xml') }}