fix retention-days

Author: chyumin

.github/workflows/test_containers_singularity.yml

@@ -29,7 +29,7 @@ jobs:
         with:
           name: docker-artifact
           path: output/docker_images
-          retention_days: 1
+          retention-days: 1
 
   test-images:
     name: Test on (${{ matrix.os }})