test(monitors): the widget's went-down time is read against the render's clock (#5250)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/core/test_monitors_page.py

@@ -153,7 +153,7 @@ async def test_the_widget_gives_a_verdict_then_problems_with_uptime_columns(app)
     and since when, then each monitor's latency and 24h/7d/30d under one header."""
     down = {**_row(_mon("api", mid="m2"), "down", _check(False)),
             "uptime": {"24h": 90.0, "7d": 97.5, "30d": 99.12},
-            "down_since": NOW - timedelta(minutes=12), "down_reason": "HTTP 503"}
+            "down_since": datetime.now(timezone.utc) - timedelta(minutes=12), "down_reason": "HTTP 503"}
     up = {**_row(_mon("web", mid="m1"), "up", _check(ms=31)), "uptime": {"24h": 100.0, "7d": 99.96}}
     page = await _widget(app, [down], [up], more=3)
     assert "1 of 5 monitors down." in page