[Bugfix][Frontend] Fix openai CLI arg middleware (#21220)

Signed-off-by: 22quinn <33176974+22quinn@users.noreply.github.com>

tests/entrypoints/openai/test_cli_args.py

@@ -153,3 +153,13 @@ def test_chat_template_validation_for_sad_paths(serve_parser):
     args = serve_parser.parse_args(args=["--chat-template", "does/not/exist"])
     with pytest.raises(ValueError):
         validate_parsed_serve_args(args)
+
+
+@pytest.mark.parametrize(
+    "cli_args, expected_middleware",
+    [(["--middleware", "middleware1", "--middleware", "middleware2"
+       ], ["middleware1", "middleware2"]), ([], [])])
+def test_middleware(serve_parser, cli_args, expected_middleware):
+    """Ensure multiple middleware args are parsed properly"""
+    args = serve_parser.parse_args(args=cli_args)
+    assert args.middleware == expected_middleware