nginx: tighten discovery E2E metric assertions from at_least=0 to at_least=1

at_least=0 can never fail — zero metrics always satisfies the condition,
so the test only verified the agent connected, not that discovery rendered
a working instance that actually scrapes metrics. at_least=1 ensures a
regression where discovery connects but emits nothing is caught loudly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: martavicentenavarro

nginx/tests/test_e2e.py

@@ -27,9 +27,9 @@ def test_e2e_discovery(dd_agent_check_discovery):
     aggregator = dd_agent_check_discovery(check_rate=True)
 
     for m in ('nginx.net.conn_dropped_per_s', 'nginx.net.conn_opened_per_s', 'nginx.net.request_per_s'):
-        aggregator.assert_metric(m, at_least=0)
+        aggregator.assert_metric(m, at_least=1)
     for m in ('nginx.net.writing', 'nginx.net.reading', 'nginx.net.waiting', 'nginx.net.connections'):
-        aggregator.assert_metric(m, at_least=0)
+        aggregator.assert_metric(m, at_least=1)
 
     aggregator.assert_service_check('nginx.can_connect', status=Nginx.OK)