fuuko/mqtt: Make compatible with Mosquitto 2

This now requires authenticating with a valid password, which it
apparently didn’t do before?

machines/fuuko/services/wordclock-dimmer.nix

@@ -12,6 +12,7 @@
         password = "ymfQkXcEqGuk62SH";
       };
     };
+    checkPasswords = true;
   };
 
   networking.firewall.allowedTCPPorts = [ 1883 ];