Same changelog as #15773

Same fix as https://github.com/matrix-org/synapse/pull/15746

Thanks to @realtyem for pointing it out!

`creatorForNetloc(...)` doesn't come with typing and expects `host`
to be `bytes` instead of a `str`.

`ProxyAgent` was introduced with the federation outbound proxy:
https://github.com/matrix-org/synapse/pull/15773

changelog.d/15886.feature

@@ -0,0 +1 @@
+Allow configuring the set of workers to proxy outbound federation traffic through via `outbound_federation_restricted_to`.

synapse/http/proxyagent.py

@@ -152,7 +152,7 @@ class ProxyAgent(_AgentBase):
 
                 if federation_proxy.tls:
                     tls_connection_creator = self._policy_for_https.creatorForNetloc(
-                        federation_proxy.host,
+                        federation_proxy.host.encode("utf-8"),
                         federation_proxy.port,
                     )
                     endpoint = wrapClientTLS(tls_connection_creator, endpoint)