build(ci): ensure echoserver healthy before testing

The integration tests now wait for the echoserver containers to be
healthy before running. This should avoid tests failing due to failing
to connect to the echoserver(s) while they're starting.

For example: https://github.com/h4l/v8serialize/actions/runs/12533338515/job/34952929385

.github/workflows/main.yml

@@ -6,7 +6,7 @@ on:
   pull_request:
 
 env:
-  ECHOSERVER_VERSION: 0.2.0
+  ECHOSERVER_VERSION: 0.3.0
 
 jobs:
   prepare_checks:

docker-compose.yml

@@ -28,9 +28,12 @@ services:
     environment:
       V8SERIALIZE_ECHOSERVERS: "${V8SERIALIZE_ECHOSERVERS:-__required_but_not_set__}"
     depends_on:
-      - echoserver-node-22
-      - echoserver-node-18
-      - echoserver-deno
+      echoserver-node-22:
+        condition: service_healthy
+      echoserver-node-18:
+        condition: service_healthy
+      echoserver-deno:
+        condition: service_healthy
     command: pytest -m integration -vv
     volumes:
       - .:${WORKSPACE_MOUNT_PATH:-/workspace}