nixos/spamassassin: Run sa-compile after updating the rules

sa-compile speeds up processing the rules by compiling them from Perl to
C.  This needs to be run after every update and is saved in the local
state directory by Perl and SpamAssassin version.

nixos/modules/services/mail/spamassassin.nix

@@ -135,7 +135,10 @@ in
         User = "spamd";
         Group = "spamd";
         StateDirectory = "spamassassin";
-        ExecStart = "${pkgs.spamassassin}/bin/sa-update --verbose --gpghomedir=%S/spamassassin/sa-update-keys/";
+        ExecStart = [
+          "${pkgs.spamassassin}/bin/sa-update --verbose --gpghomedir=%S/spamassassin/sa-update-keys/"
+          "${pkgs.spamassassin}/bin/sa-compile"
+        ];
         ExecStartPost = "+${pkgs.systemd}/bin/systemctl -q --no-block try-reload-or-restart spamd.service";
         SuccessExitStatus = "1";
       };