Remove dangling layers.

Author: ggorman

.github/workflows/docker-devito.yml

@@ -112,7 +112,6 @@ jobs:
           build-args: base=devitocodes/${{ matrix.base }}
 
       - name: Remove dangling layers
-        if: ${{ !contains(matrix.runner, 'nvidiagpu') }}
         run: docker system prune -f
 
       - name: Run tests

.github/workflows/pytest-gpu.yml

@@ -124,3 +124,10 @@ jobs:
         run: |
           docker run ${{ matrix.flags }} --env DEVITO_MPI=1 "${DOCKER_IMAGE}" \
             mpiexec -n 2 pytest ${{ matrix.test_examples }}
+
+      - name: Clean up test image
+        if: always()
+        run: |
+          docker rmi -f "${DOCKER_IMAGE}" || true     # drop the tag
+          docker system prune -f                      # free dangling layers
+