Strip trailing whitespaces in submodule URLs

Users attempting to access repositories that had `.gitmodules` entries
with trailing whitespaces would encounter an Error 500. This was due
to a change in bf876ec7 that quietly removed the whitespace stripping.

Closes #33018

app/helpers/submodule_helper.rb

@@ -13,6 +13,7 @@ module SubmoduleHelper
 
     if url =~ /([^\/:]+)\/([^\/]+(?:\.git)?)\Z/
       namespace, project = $1, $2
+      project.rstrip!
       project.sub!(/\.git\z/, '')
 
       if self_url?(url, namespace, project)

changelogs/unreleased/sh-fix-submodules-trailing-spaces.yml

+---
+title: Strip trailing whitespaces in submodule URLs
+merge_request:
+author:

spec/helpers/submodule_helper_spec.rb

@@ -115,6 +115,11 @@ describe SubmoduleHelper do
         expect(submodule_links(submodule_item)).to eq(['https://gitlab.com/gitlab-org/gitlab-ce', 'https://gitlab.com/gitlab-org/gitlab-ce/tree/hash'])
       end
 
+      it 'handles urls with trailing whitespace' do
+        stub_url('http://gitlab.com/gitlab-org/gitlab-ce.git  ')
+        expect(submodule_links(submodule_item)).to eq(['https://gitlab.com/gitlab-org/gitlab-ce', 'https://gitlab.com/gitlab-org/gitlab-ce/tree/hash'])
+      end
+
       it 'returns original with non-standard url' do
         stub_url('http://gitlab.com/another/gitlab-org/gitlab-ce.git')
         expect(submodule_links(submodule_item)).to eq([repo.submodule_url_for, nil])