Fix tests by downgrading pytest-asyncio

dev-requirements.txt

@@ -1,7 +1,7 @@
 pytest==8.3.2
 flake8==7.1.0
 pytest-timeout==2.3.1
-pytest-asyncio==0.23.8
+pytest-asyncio==0.21.2
 requests==2.32.3
 httpx==0.24.1 # version 0.24.1 is required by httpx_ws
 httpx_ws==0.4.2