ci: Fix cache in eic build (acts-project#4760)

Author: paulgessinger

.github/workflows/builds.yml

@@ -408,7 +408,7 @@ jobs:
         continue-on-error: true
         with:
           image: "ghcr.io/eic/eic_ci_without_acts:nightly"
-          options: -v ${{ github.workspace }}:/work
+          options: -v ${{ github.workspace }}:/work -v ${{ env.CCACHE_DIR }}:/root/.cache/ccache
           shell: bash
           run: |
             for script in /.singularity.d/env/*.sh; do
@@ -420,6 +420,7 @@ jobs:
             set -ue
 
             pushd acts
+            ccache -p | grep cache_dir
             ccache -z && \
             export CMAKE_INSTALL_PREFIX=$HOME/prefix
             export CMAKE_CXX_COMPILER_LAUNCHER=ccache