git: Add configured SSL certificate for SMTP (#1833)

If you have a custom SSL certificate configured for SMTP TLS, git should
use it.

modules/programs/git.nix

@@ -290,6 +290,7 @@ in {
                   "ssl")
               else
                 "";
+              smtpSslCertPath = mkIf smtp.tls.enable smtp.tls.certificatesFile;
               smtpServer = smtp.host;
               smtpUser = userName;
               from = address;