Fix tab arrows on RTL layouts (#24520)

app/javascript/styles/mastodon/components.scss

@@ -6685,7 +6685,7 @@ a.status-card.compact:hover {
         content: '';
         position: absolute;
         bottom: 0;
-        inset-inline-start: 50%;
+        left: 50%;
         width: 0;
         height: 0;
         transform: translateX(-50%);