Fix NoMethodError for RefsController

Contributes to https://gitlab.com/gitlab-org/gitlab/-/issues/351520

Fix a typo and add a test

Changelog: fixed

app/controllers/projects/refs_controller.rb

@@ -62,6 +62,6 @@ class Projects::RefsController < Projects::ApplicationController
   private
 
   def validate_ref_id
-    return not_found! if params[:id].present? && params[:id] !~ Gitlab::PathRegex.git_reference_regex
+    return not_found if params[:id].present? && params[:id] !~ Gitlab::PathRegex.git_reference_regex
   end
 end

spec/controllers/projects/refs_controller_spec.rb

@@ -47,6 +47,14 @@ RSpec.describe Projects::RefsController do
       expect(response).to be_not_found
     end
 
+    context 'when ref is incorrect' do
+      it 'returns 404 page' do
+        xhr_get(:json, id: '.')
+
+        expect(response).to be_not_found
+      end
+    end
+
     context 'when json is requested' do
       it 'renders JSON' do
         expect(::Gitlab::GitalyClient).to receive(:allow_ref_name_caching).and_call_original