Move reliable tag to specific test

This way, only one test in the suite is considered reliable,
instead of both.

The reason for this change is that the test that comments on an
issue with an attachment has failed in the following reliable job:

https://ops.gitlab.net/gitlab-org/quality/canary/-/jobs/907724

And so it can't be considered reliable.

qa/qa/specs/features/browser_ui/2_plan/issue/create_issue_spec.rb

 # frozen_string_literal: true
 
 module QA
-  context 'Plan', :smoke, :reliable do
+  context 'Plan', :smoke do
     describe 'Issue creation' do
       before do
         Flow::Login.sign_in
       end
 
-      it 'creates an issue' do
+      it 'creates an issue', :reliable do
         issue = Resource::Issue.fabricate_via_browser_ui!
 
         Page::Project::Menu.perform(&:click_issues)