Add type annotations to extra_args in generated_client

Co-authored-by: dbanty <43723790+dbanty@users.noreply.github.com>

Author: Copilot

end_to_end_tests/generated_client.py

@@ -85,7 +85,7 @@ def _run_command(
 
 def generate_client(
     openapi_document: str | Path,
-    extra_args=None,
+    extra_args: list[str] | None = None,
     output_path: str = "my-test-api-client",
     base_module: str = "my_test_api_client",
     overwrite: bool = True,
@@ -113,7 +113,7 @@ def generate_client(
 
 def generate_client_from_inline_spec(
     openapi_spec: str,
-    extra_args=None,
+    extra_args: list[str] | None = None,
     config: str = "",
     filename_suffix: str | None = None,
     base_module: str = "testapi_client",