fix: update NixOS channel references to version 25.05 and adjust netdata configuration

hosts/mail/modules/dovecot.nix

@@ -88,6 +88,7 @@ in
 {
   environment.systemPackages = with pkgs; [
     doveSync
+    dovecot_pigeonhole
   ];
 
   services.dovecot2 = {
@@ -215,9 +216,6 @@ in
       # Read multiple mails in parallel, improves performance
       mail_prefetch_count = 20
     '';
-    modules = [
-      pkgs.dovecot_pigeonhole
-    ];
     protocols = [
       "sieve"
     ];