ci(test): migrate docker image for testing to bitnamilegacy repo (#355)

Author: LiteSun

libs/backend-apisix/e2e/assets/docker-compose.yaml

@@ -27,7 +27,7 @@ services:
       apisix:
 
   etcd:
-    image: bitnami/etcd:3.5
+    image: bitnamilegacy/etcd:3.5
     restart: always
     volumes:
       - etcd_data:/bitnami/etcd