Do not allow staff_user_id to be mutated (#6009) [deploy]

Allowing ids to be mutated by admins from the /internal/config pages is dangerous.
This could cause issues if an admin tries to update the SiteConfig.staff_user_id to an id that is another user's id, or to an id that isn't valid.

app/controllers/internal/configs_controller.rb

@@ -18,7 +18,7 @@ class Internal::ConfigsController < Internal::ApplicationController
 
   def config_params
     allowed_params = %i[
-      staff_user_id default_site_email social_networks_handle
+      default_site_email social_networks_handle
       main_social_image favicon_url logo_svg
       rate_limit_follow_count_daily
       ga_view_id ga_fetch_rate

app/views/internal/configs/show.html.erb

@@ -12,16 +12,6 @@
       <div class="card mt-3">
         <div class="card-header">Staff</div>
         <div class="card-body">
-          <div class="form-group">
-            <%= f.label :staff_user_id %>
-            <%= f.number_field :staff_user_id,
-                               class: "form-control",
-                               value: SiteConfig.staff_user_id,
-                               min: 1,
-                               placeholder: "1" %>
-            <div class="alert alert-info">User ID of the staff account</div>
-          </div>
-
           <div class="form-group">
             <%= f.label :default_site_email %>
             <%= f.email_field :default_site_email,

spec/requests/internal/configs_spec.rb

@@ -20,9 +20,10 @@ RSpec.describe "/internal/config", type: :request do
     end
 
     describe "staff" do
-      it "updates staff_user_id" do
+      it "does not allow the staff_user_id to be updated" do
+        expect(SiteConfig.staff_user_id).to eq(1)
         post "/internal/config", params: { site_config: { staff_user_id: 2 } }
-        expect(SiteConfig.staff_user_id).to eq(2)
+        expect(SiteConfig.staff_user_id).to eq(1)
       end
 
       it "updates default_site_email" do