gha: test: sleep after foreground test so Docker can cleanup; kill it -9; stop and remove it after timeout

Author: rpardini

.github/workflows/test.yaml

@@ -44,12 +44,14 @@ jobs:
 
       - name: Start foreground instance for first-contact sanity checking
         run: |
-          timeout --verbose 10 docker run \
+          timeout --signal=9 --verbose 10 docker run --name docker_registry_proxy_fg \
             -p 0.0.0.0:3128:3128 -e ENABLE_MANIFEST_CACHE=false \
             -v $(pwd)/docker_mirror_cache:/docker_mirror_cache \
             -v $(pwd)/docker_mirror_certs:/ca \
             sanity-check/docker-registry-proxy:latest || true
-          sleep 5
+          sleep 3
+          docker stop docker_registry_proxy_fg || true
+          docker remote docker_registry_proxy_fg || true
 
       - name: Start proxy instance in docker (ENABLE_MANIFEST_CACHE=false)
         run: |