Merge branch '39653-hide-section_start-and-section_end-in-pipeline-emails' into 'master'

Resolve "Hide `section_start` and `section_end` in pipeline emails"

Closes #39653

See merge request gitlab-org/gitlab-ce!15534

app/views/layouts/_mailer.html.haml

@@ -10,6 +10,10 @@
       body, table, td, a { -webkit-text-size-adjust: 100%; -ms-text-size-adjust: 100%; }
       table, td { mso-table-lspace: 0pt; mso-table-rspace: 0pt; }
       img { -ms-interpolation-mode: bicubic; }
+      .hidden {
+          display: none !important;
+          visibility: hidden !important;
+      }
 
       /* iOS BLUE LINKS */
       a[x-apple-data-detectors] {