Update Docker images (#524)

pkg/runner/testdata/actions/docker-local/Dockerfile

@@ -1,5 +1,5 @@
 # Container image that runs your code
-FROM alpine:3.10
+FROM alpine:3.13
 
 # Copies your code file from your action repository to the filesystem path `/` of the container
 COPY entrypoint.sh /entrypoint.sh

pkg/runner/testdata/actions/docker-url/action.yml

@@ -8,7 +8,7 @@ inputs:
     default: World
 runs:
   using: docker
-  #image: docker://alpine:3.8
+  #image: docker://alpine:3.13
   image: docker://node:12-alpine
   env:
     TEST: enabled