Add --http2-max-concurrent-streams server arg (#34796)

Co-authored-by: Yilong Zhao <74357408+happierpig@users.noreply.github.com>

test/registered/openai_server/basic/test_http2_server.py

@@ -41,7 +41,11 @@ class TestHTTP2Server(CustomTestCase):
             cls.model,
             cls.base_url,
             timeout=DEFAULT_TIMEOUT_FOR_SERVER_LAUNCH,
-            other_args=["--enable-http2"],
+            other_args=[
+                "--enable-http2",
+                "--http2-max-concurrent-streams",
+                "64",
+            ],
         )
 
     @classmethod
@@ -126,7 +130,13 @@ class TestHTTP2ServerMultiTokenizer(TestHTTP2Server):
             cls.model,
             cls.base_url,
             timeout=DEFAULT_TIMEOUT_FOR_SERVER_LAUNCH,
-            other_args=["--enable-http2", "--tokenizer-worker-num", "2"],
+            other_args=[
+                "--enable-http2",
+                "--http2-max-concurrent-streams",
+                "64",
+                "--tokenizer-worker-num",
+                "2",
+            ],
         )