Avoid flakiness in test_timeline_delete_fail_before_local_delete (#5032)

The problem was that timeline detail can return timelines in not only
active state. And by the time request comes timeline deletion can still
be in progress if we're unlucky (test execution happened to be slower
for some reason)

Reference for failed test run

https://neon-github-public-dev.s3.amazonaws.com/reports/pr-5022/5891420105/index.html#suites/f588e0a787c49e67b29490359c589fae/dab036e9bd673274

The error was `Exception: detail succeeded (it should return 404)`

reported by @koivunej

pageserver/src/http/routes.rs

@@ -517,7 +517,6 @@ async fn timeline_delete_handler(
         .instrument(info_span!("timeline_delete", %tenant_id, %timeline_id))
         .await?;
 
-    // FIXME: needs to be an error for console to retry it. Ideally Accepted should be used and retried until 404.
     json_response(StatusCode::ACCEPTED, ())
 }
 

test_runner/regress/test_timeline_delete.py

@@ -488,15 +488,7 @@ def test_timeline_delete_fail_before_local_delete(neon_env_builder: NeonEnvBuild
     # Wait for tenant to finish loading.
     wait_until_tenant_active(ps_http, tenant_id=env.initial_tenant, iterations=10, period=1)
 
-    try:
-        data = ps_http.timeline_detail(env.initial_tenant, leaf_timeline_id)
-        log.debug(f"detail {data}")
-    except PageserverApiException as e:
-        log.debug(e)
-        if e.status_code != 404:
-            raise
-    else:
-        raise Exception("detail succeeded (it should return 404)")
+    wait_timeline_detail_404(ps_http, env.initial_tenant, leaf_timeline_id, iterations=4)
 
     assert (
         not leaf_timeline_path.exists()