update-nixpkgs: The httpx client changed its public interface

https://github.com/encode/httpx/blob/master/CHANGELOG.md
> The allow_redirects flag is now follow_redirects and defaults to False.

[...]

> The raise_for_status() method will now raise an exception for any responses
> except those with 2xx status codes. Previously only 4xx and 5xx status codes
> would result in an exception.

tools/update-nixpkgs

@@ -10,7 +10,7 @@ from ps_tools import get_url_hash
 # We pass this to builtins.fetchTarball which only supports sha256
 HASH_TYPE = "sha256"
 
-DEFAULT_CHANNEL = "nixos-21.11"
+DEFAULT_CHANNEL = "nixos-22.11"
 CHANNEL_URL_TEMPLATE = "https://channels.nixos.org/{channel}/nixexprs.tar.xz"
 
 
@@ -24,9 +24,8 @@ def get_nixos_channel_url(*, channel):
     the release.
     """
     response = httpx.head(
-        CHANNEL_URL_TEMPLATE.format(channel=channel), allow_redirects=False
+        CHANNEL_URL_TEMPLATE.format(channel=channel), follow_redirects=False
     )
-    response.raise_for_status()
     assert response.is_redirect
     return str(response.next_request.url)