fix(ci): add matrix.release to ccache key (#1425)

### Briefly, what does this PR introduce?
This PR adds the release environment name to the ccache key to ensure
that eic_xl:nightly and eic_xl:24.04.0-stable each get a separate
ccache.

### What kind of change does this PR introduce?
- [x] Bug fix (issue: failed ccache writes, e.g.
https://github.com/eic/EICrecon/actions/runs/8977682643/job/24656865794?pr=1418#step:27:3,
and slow eic_xl:24.04.0-stable builds)
- [ ] New feature (issue #__)
- [ ] Documentation update
- [ ] Other: __

### Please check if this PR fulfills the following:
- [ ] Tests for the changes have been added
- [ ] Documentation has been added / updated
- [ ] Changes have been communicated to collaborators

### Does this PR introduce breaking changes? What changes might users
need to make to their code?
No.

### Does this PR change default behavior?
No.

.github/workflows/linux-eic-shell.yml

@@ -102,12 +102,13 @@ jobs:
       uses: actions/cache@v4
       with:
         path: .ccache
-        key: ccache-${{ matrix.CC }}-${{ matrix.CMAKE_BUILD_TYPE }}-${{ github.event.pull_request.head.ref || github.ref_name }}-${{ steps.ccache_cache_timestamp.outputs.timestamp }}
+        key: ccache-${{ matrix.CC }}-${{ matrix.release }}-${{ matrix.CMAKE_BUILD_TYPE }}-${{ github.event.pull_request.head.ref || github.ref_name }}-${{ steps.ccache_cache_timestamp.outputs.timestamp }}
         restore-keys: |
-             ccache-${{ matrix.CC }}-${{ matrix.CMAKE_BUILD_TYPE }}-${{ github.ref_name }}-
-             ccache-${{ matrix.CC }}-${{ matrix.CMAKE_BUILD_TYPE }}-${{ github.event.pull_request.head.ref }}-
-             ccache-${{ matrix.CC }}-${{ matrix.CMAKE_BUILD_TYPE }}-${{ github.event.pull_request.base.ref }}-
-             ccache-${{ matrix.CC }}-${{ matrix.CMAKE_BUILD_TYPE }}-
+             ccache-${{ matrix.CC }}-${{ matrix.release }}-${{ matrix.CMAKE_BUILD_TYPE }}-${{ github.ref_name }}-
+             ccache-${{ matrix.CC }}-${{ matrix.release }}-${{ matrix.CMAKE_BUILD_TYPE }}-${{ github.event.pull_request.head.ref }}-
+             ccache-${{ matrix.CC }}-${{ matrix.release }}-${{ matrix.CMAKE_BUILD_TYPE }}-${{ github.event.pull_request.base.ref }}-
+             ccache-${{ matrix.CC }}-${{ matrix.release }}-${{ matrix.CMAKE_BUILD_TYPE }}-
+             ccache-${{ matrix.CC }}-${{ matrix.release }}-
              ccache-${{ matrix.CC }}-
              ccache-
     - name: Configure ccache