Simplify docker tests

Only the healthcheck is really necessary for the workflow's purpose.
Running the full test suite is redundant.

.github/workflows/docker_tests.yml

@@ -11,9 +11,6 @@ jobs:
     - name: build and test
       run: |
         docker build --tag whoogle-search:test .
-        TEST_CONTAINER=$(docker run --entrypoint=/bin/bash --detach whoogle-search:test)
+        docker run --publish 5000:5000 --detach --name whoogle-search whoogle-search:test
-        docker cp test "$TEST_CONTAINER":/whoogle/test
+        sleep 15
-        docker exec "$TEST_CONTAINER" ./run test
+        docker exec whoogle-search curl -f http://localhost:5000/healthz || exit 1
-        docker exec --detach "$TEST_CONTAINER" ./run
-        sleep 10
-        docker exec "$TEST_CONTAINER" curl -f http://localhost:5000/healthz || exit 1