redis: switch to valkey

hosts/arashi/services/redis.nix

@@ -1,6 +1,8 @@
 {pkgs, ...}: {
   environment.systemPackages = [pkgs.redis-dump];
-  services.redis.servers = {
+  services.redis = {
+    package = pkgs.valkey;
+    servers = {
       forgejo = {
         enable = true;
         openFirewall = true;
@@ -50,4 +52,5 @@
         };
       };
     };
+  };
 }