test(tokenlab): follow the unit test layout and drop an unused suppression

The provider test moves next to the other OpenAI-like provider tests under
tests/unit, which is where the CI shards look for them. The `mutable-ok`
marker on `tokenlab_models` suppressed nothing, so the type discipline
gate reported it as LIT013; the line now matches its neighbours.

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

litellm/__init__.py

@@ -687,7 +687,7 @@ qwen_ai_platform_models: Set = set()
 moonshot_models: Set = set()
 publicai_models: Set = set()
 darkbloom_models: Set = set()
-tokenlab_models: Set = set()  # mutable-ok: populated while loading the static model registry
+tokenlab_models: Set = set()
 v0_models: Set = set()
 morph_models: Set = set()
 lambda_ai_models: Set = set()