Update docker.elastic.co/elasticsearch/elasticsearch Docker tag to v8

Author: renovate[bot]

Diff for: .github/workflows/ci.yml

@@ -26,7 +26,7 @@ jobs:
           - 6379:6379
 
       elastic:
-        image: docker.elastic.co/elasticsearch/elasticsearch:6.7.1
+        image: docker.elastic.co/elasticsearch/elasticsearch:8.12.1
         env:
           network.host: "0.0.0.0"
           http.cors.enabled: "true"