Pin httpx to < 0.20
0.20.0 drops timeout parameter from .send():
https://github.com/encode/httpx/commit/ff9813e84dab56f0f3c4ef3a159a4cce8c644a91
0.20.0 drops timeout parameter from .send():
https://github.com/encode/httpx/commit/ff9813e84dab56f0f3c4ef3a159a4cce8c644a91