use the submodule commit as the test data cache key (#113)

.github/workflows/actions.yml

@@ -29,12 +29,19 @@ jobs:
           mamba-version: "*"
           environment-file: environment.yml
 
+      - name: Generate cache key for submodule
+        id: generate-cache-key
+        run: |
+          # Get the submodule commit SHA
+          SUBMODULE_SHA=$(git submodule status | awk '{print $1}' | sha256sum | cut -d ' ' -f 1)
+          echo "SUBMODULE_KEY=$SUBMODULE_SHA" >> $GITHUB_ENV
+
       - name: Restore/save LFS files in cache
         id: cache-lfs
         uses: actions/cache@v4
         with:
           path: test/data/reflectivity_ui-data/
-          key: ${{ runner.os }}-lfs-files
+          key: submodule-${{ env.SUBMODULE_KEY }}
 
       - name: Pull LFS files for the submodule
         if: steps.cache-lfs.outputs.cache-hit != 'true'