Fix Project#pages_url not to downcase url path

In https://gitlab.com/gitlab-org/gitlab/-/merge_requests/35300 we fixed
how to handle group root Pages with mixed case path, but the
fix broke how we generate #pages_url for project level with mixed case.

This updates Project#pages_url so that we downcase only when comparing
with #pages_group_url and retrun the original url path if the project
is not group root Pages project.

Related to https://gitlab.com/gitlab-org/gitlab/-/issues/226874.

app/models/project.rb

@@ -1700,10 +1700,10 @@ class Project < ApplicationRecord
 
   def pages_url
     url = pages_group_url
-    url_path = full_path.partition('/').last.downcase
+    url_path = full_path.partition('/').last
 
     # If the project path is the same as host, we serve it as group page
-    return url if url == "#{Settings.pages.protocol}://#{url_path}"
+    return url if url == "#{Settings.pages.protocol}://#{url_path}".downcase
 
     "#{url}/#{url_path}"
   end

changelogs/unreleased/226874-fix-pages-url-path.yml

+---
+title: Fix Project#pages_url not to downcase url path
+merge_request: 36183
+author:
+type: fixed

spec/models/project_spec.rb

@@ -1666,6 +1666,14 @@ RSpec.describe Project do
       let(:project_name) { 'Project' }
 
       it { is_expected.to eq("http://group.example.com/project") }
+
+      context 'mixed case path' do
+        before do
+          project.update!(path: 'Project')
+        end
+
+        it { is_expected.to eq("http://group.example.com/Project") }
+      end
     end
   end