tag: fix multiple issues grouping (#1997) (#2003)

Fix regression where section-specific tags were no longer ignored due to
a change in the HTML structure of article headings.

modules/friendlytag.js

@@ -315,7 +315,7 @@ Twinkle.tag.callback = function friendlytagCallback() {
 
 				// break out on encountering the first heading, which means we are no
 				// longer in the lead section
-				if (e.tagName === 'H2') {
+				if (e.classList.contains('mw-heading')) {
 					return false;
 				}