Set customize_hostname_check for Swoosh.Adapters.SMTP

This should hopefully fix issues with connecting to SMTP servers
with wildcard TLS certificates.

Taken from https://erlef.github.io/security-wg/secure_coding_and_deployment_hardening/ssl

Fixes AkkomaGang/akkoma#660

lib/pleroma/emails/mailer.ex

@@ -86,6 +86,9 @@ defp default_config(Swoosh.Adapters.SMTP, conf, _) do
       verify: :verify_peer,
       # some versions have supposedly issues verifying wildcard certs without this
       server_name_indication: relay,
+      customize_hostname_check: [
+        match_fun: :public_key.pkix_verify_hostname_match_fun(:https)
+      ],
       # the default of 10 is too restrictive
       depth: 32
     ]