bump version to 9.0.4 and run make check-ci (#8714)

Author: pkoutsovasilis

testing/integration/k8s/testdata/elastic-agent-kustomize.yaml

@@ -730,7 +730,7 @@ spec:
             configMapKeyRef:
               key: ca_trusted
               name: elastic-agent-configs-k799f79hhb
-        image: docker.elastic.co/elastic-agent/elastic-agent:9.0.3
+        image: docker.elastic.co/elastic-agent/elastic-agent:9.0.4
         name: elastic-agent-standalone
         resources:
           limits: