Fix OAuth auth flow tests to properly close async generators

The retry logic fix in PR-1206 moved the final request yield inside the OAuth
flow block, which now correctly retries requests after OAuth completion.
However, the existing tests didn't expect this final yield and would exit
the generator early, causing a GeneratorExit exception while the async lock
was still held. This resulted in RuntimeError: The current task is not
holding this lock.

Fix by properly closing the generators in both failing tests:
- test_oauth_discovery_fallback_conditions
- test_auth_flow_with_no_tokens

Both tests now send a final success response to properly complete the
auth flow generator and prevent the lock release error.

Author: felixweinberger

tests/client/test_auth.py

@@ -361,7 +361,19 @@ async def test_oauth_discovery_fallback_conditions(self, oauth_provider: OAuthCl
             ),
             request=token_request,
         )
-        token_request = await auth_flow.asend(token_response)
+        
+        # After OAuth flow completes, the original request is retried with auth header
+        final_request = await auth_flow.asend(token_response)
+        assert final_request.headers["Authorization"] == "Bearer new_access_token"
+        assert final_request.method == "GET"
+        assert str(final_request.url) == "https://api.example.com/v1/mcp"
+        
+        # Send final success response to properly close the generator
+        final_response = httpx.Response(200, request=final_request)
+        try:
+            await auth_flow.asend(final_response)
+        except StopAsyncIteration:
+            pass  # Expected - generator should complete
 
     @pytest.mark.anyio
     async def test_handle_metadata_response_success(self, oauth_provider: OAuthClientProvider):
@@ -694,6 +706,13 @@ async def test_auth_flow_with_no_tokens(self, oauth_provider: OAuthClientProvide
         assert final_request.method == "GET"
         assert str(final_request.url) == "https://api.example.com/mcp"
 
+        # Send final success response to properly close the generator
+        final_response = httpx.Response(200, request=final_request)
+        try:
+            await auth_flow.asend(final_response)
+        except StopAsyncIteration:
+            pass  # Expected - generator should complete
+
         # Verify tokens were stored
         assert oauth_provider.context.current_tokens is not None
         assert oauth_provider.context.current_tokens.access_token == "new_access_token"