Replace some gt- classes with tw- (#29570)

Replace 18 `gt-` prefixes with `tw-` with perl replacement. I manually
checked them all with `rg` afterwards.

templates/repo/diff/comment_form.tmpl

@@ -27,7 +27,7 @@
 
 		<div class="field footer gt-mx-3">
 			<span class="markup-info">{{svg "octicon-markup"}} {{ctx.Locale.Tr "repo.diff.comment.markdown_info"}}</span>
-			<div class="gt-text-right">
+			<div class="tw-text-right">
 				{{if $.reply}}
 					<button class="ui submit primary tiny button btn-reply" type="submit">{{ctx.Locale.Tr "repo.diff.comment.reply"}}</button>
 					<input type="hidden" name="reply" value="{{$.reply}}">