ci(gateway): run tests/test_gateway in the proxy-infra shard and justify the mock usage cast

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

.github/workflows/test-unit.yml

@@ -200,6 +200,7 @@ jobs:
               tests/test_litellm/proxy/types_utils
               tests/test_litellm/proxy/logging_endpoints
               tests/test_litellm/proxy/test_*.py
+              tests/test_gateway
             workers: 4
             reruns: 2
             timeout-minutes: 20

litellm/main.py

@@ -5565,7 +5565,9 @@ def completion(
                 custom_llm_provider=custom_llm_provider,
                 mock_timeout=mock_timeout,
                 timeout=timeout,
-                prompt_tokens=admission_input_tokens(cast(Mapping[str, object], kwargs)),
+                prompt_tokens=admission_input_tokens(
+                    cast(Mapping[str, object], kwargs)  # cast-ok: completion's **kwargs is untyped
+                ),
             )
 
         ## RESPONSES API BRIDGE LOGIC ## - check if model has 'mode: responses' in litellm.model_cost map