Update text color of upgrade section

app/views/shared/empty_states/_issues.html.haml

@@ -54,7 +54,7 @@
           - jira_docs_link_url = help_page_url('user/project/integrations/jira', anchor: 'view-jira-issues-premium')
           - jira_docs_link_start = '<a href="%{url}" target="_blank" rel="noopener noreferrer">'.html_safe % { url: jira_docs_link_url }
           = html_escape(s_('JiraService|%{jira_docs_link_start}Enable the Jira integration%{jira_docs_link_end} to view your Jira issues in GitLab.')) % { jira_docs_link_start: jira_docs_link_start.html_safe, jira_docs_link_end: '</a>'.html_safe }
-        %p.gl-text-center.gl-mb-0
+        %p.gl-text-center.gl-mb-0.gl-text-gray-500
           = s_('JiraService|This feature requires a Premium plan.')
 
       - else