Fix background of signed-commits on arc-green (#12837)

Signed-off-by: Andrew Thornton <art27@cantab.net>

web_src/less/themes/theme-arc-green.less

@@ -1490,7 +1490,8 @@ a.ui.labels .label:hover {
 }
 
 .repository #commits-table td.sha .sha.label.isSigned .detail.icon,
-.repository #repo-files-table .sha.label.isSigned .detail.icon {
+.repository #repo-files-table .sha.label.isSigned .detail.icon,
+.repository .timeline-item.commits-list .singular-commit .sha.label.isSigned .detail.icon {
   background: none;
   border-left-color: #888;
 }