test(header): assert every catalogue follows the palette gradient

tests/test_providers.py

@@ -154,7 +154,7 @@ def test_tilderadio_replaces_the_station_list_with_a_schedule() -> None:
     provider = TilderadioProvider()
     assert provider.has_schedule is True
     # the SomaFM wordmark's slot now holds tilderadio's own art and motto
-    assert provider.hero and not provider.hero_gradient
+    assert provider.hero and provider.hero_gradient
     assert provider.hero_lines == (
         "TILDERADIO",
         "STREAMED BY / FOR USERS OF THE",