FIX: Theme import error handling needs to happen inside the hijack block (#18866)

Otherwise the errors don't get caught.

app/controllers/admin/themes_controller.rb

@@ -97,15 +97,14 @@ class Admin::ThemesController < Admin::AdminController
         return
       end
 
+      hijack do
         begin
           branch = params[:branch] ? params[:branch] : nil
           private_key = params[:public_key] ? Discourse.redis.get("ssh_key_#{params[:public_key]}") : nil
           return render_json_error I18n.t("themes.import_error.ssh_key_gone") if params[:public_key].present? && private_key.blank?
 
-        hijack do
           @theme = RemoteTheme.import_theme(remote, theme_user, private_key: private_key, branch: branch)
           render json: @theme, status: :created
-        end
         rescue RemoteTheme::ImportError => e
           if params[:force]
             theme_name = params[:remote].gsub(/.git$/, "").split("/").last
@@ -125,6 +124,7 @@ class Admin::ThemesController < Admin::AdminController
             render_json_error e.message
           end
         end
+      end
     elsif params[:bundle] || (params[:theme] && THEME_CONTENT_TYPES.include?(params[:theme].content_type))
 
       ban_in_allowlist_mode!

spec/requests/admin/themes_controller_spec.rb

@@ -230,6 +230,14 @@ RSpec.describe Admin::ThemesController do
         expect(response.status).to eq(201)
       end
 
+      it 'fails to import with a failing status' do
+        post "/admin/themes/import.json", params: {
+          remote: 'non-existant'
+        }
+
+        expect(response.status).to eq(422)
+      end
+
       it 'can lookup a private key by public key' do
         Discourse.redis.setex('ssh_key_abcdef', 1.hour, 'rsa private key')