Fix partial not existing in FOSS

Resolves https://gitlab.com/gitlab-org/gitlab/-/issues/229728

app/views/notify/merge_when_pipeline_succeeds_email.html.haml

@@ -148,9 +148,7 @@
                                             %a.muted{ href: user_url(assignee), style: "color: #333333; text-decoration: none; -webkit-text-size-adjust: 100%; -ms-text-size-adjust: 100%; vertical-align: top;" }
                                               = assignee.name
 
-        -# EE-specific start
-        = render 'layouts/mailer/additional_text'
-        -# EE-specific end
+        = render_if_exists 'layouts/mailer/additional_text'
 
         %tr.footer
           %td{ style: "font-family:'Helvetica Neue',Helvetica,Arial,sans-serif;padding:25px 0;font-size:13px;line-height:1.6;color:#5c5c5c;" }