gitea: Use a defined service UID

The default of 1000 mapped to my admin user, which was both a bit
concerning and a bit of an annoyance.

configuration/services/gitea.nix

@@ -3,11 +3,12 @@
 {
   users = {
     extraUsers.gitea = {
+      uid = config.ids.uids.git;
       isSystemUser = true;
       description = "Gitea Service";
       group = config.users.extraGroups.gitea.name;
     };
-    extraGroups.gitea = { };
+    extraGroups.gitea = { gid = config.ids.gids.git; };
   };
 
   virtualisation.pods.gitea = {