Pin httpx till upstream gets resolved (#3465)

Author: sl0thentr0py

tox.ini

@@ -629,7 +629,7 @@ deps =
     starlette: pytest-asyncio
     starlette: python-multipart
     starlette: requests
-    starlette: httpx
+    starlette: httpx<0.27.1
     # (this is a dependency of httpx)
     starlette: anyio<4.0.0
     starlette: jinja2