Merge branch 'fix-mr-tabs' into 'master'

Fix MR tabs bottom border

Closes #46764

See merge request gitlab-org/gitlab-ce!19446

app/assets/stylesheets/bootstrap_migration.scss

@@ -224,6 +224,9 @@ table {
 }
 
 .nav-tabs {
+  // Override bootstrap's default border
+  border-bottom: 0;
+
   .nav-link {
     border-top: 0;
     border-left: 0;