Bump admin stylesheet cache key

tests/test_ui.py

@@ -182,7 +182,7 @@ def test_dashboard_link_can_delete_hostname(tmp_path: Path) -> None:
 
     management = client.get(f"/m/{account['management_slug']}")
     assert management.status_code == 200
-    assert '<link href="/admin.css?v=2" rel="stylesheet">' in management.text
+    assert '<link href="/admin.css?v=3" rel="stylesheet">' in management.text
     assert "home.ddns.example.net" in management.text
     assert "CNAME target:" in management.text
     assert "Router fields" in management.text