tests: cache sample files

Author: henryborchers

.github/workflows/tox_matrix.yml

@@ -48,7 +48,7 @@ jobs:
         id: cache_samples
         uses: actions/cache@v4
         with:
-          path: "{{ github.workspace }}"
+          path: "${{ github.workspace }}"
           key: sample-images-${{ hashFiles('sample_images.tar.gz') }}
       - name: download sample files
         if: steps.cache_samples.outputs.cache-hit != 'true'