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/unit-test.yaml

@@ -64,7 +64,7 @@ jobs:
     steps:
     - name: Restore cached HOOMD-blue build
       id: cache
-      uses: actions/cache/restore@v3
+      uses: actions/cache/restore@v4
       with:
         path: install
         key: hoomd-blue-${{ env.HOOMD_BLUE_VERSION }}-2023.11.27-cuda120_gcc11_py310-mpi-${{ matrix.enable_mpi }}-gpu-${{ matrix.enable_gpu }}
@@ -97,7 +97,7 @@ jobs:
       working-directory: build-hoomd-blue
     - name: Cache HOOMD-blue build
       if: steps.cache.outputs.cache-hit != 'true'
-      uses: actions/cache/save@v3
+      uses: actions/cache/save@v4
       with:
         path: install
         key: hoomd-blue-${{ env.HOOMD_BLUE_VERSION }}-2023.11.27-cuda120_gcc11_py310-mpi-${{ matrix.enable_mpi }}-gpu-${{ matrix.enable_gpu }}