Fix previous/next button size (#16284)

Author: jpraet

templates/repo/diff/conversation.tmpl

@@ -29,10 +29,10 @@
 		<div class="df je ac fw mt-3">
 			<div class="ui buttons mr-2">
 				<button class="ui icon tiny basic button previous-conversation">
-					{{svg "octicon-arrow-up"}} {{$.i18n.Tr "repo.issues.previous"}}
+					{{svg "octicon-arrow-up" 12 "icon"}} {{$.i18n.Tr "repo.issues.previous"}}
 				</button>
 				<button class="ui icon tiny basic button next-conversation">
-					{{svg "octicon-arrow-down"}} {{$.i18n.Tr "repo.issues.next"}}
+					{{svg "octicon-arrow-down" 12 "icon"}} {{$.i18n.Tr "repo.issues.next"}}
 				</button>
 			</div>
 			{{if and $.CanMarkConversation $isNotPending}}