Fix sign up steps progress layout in right-to-left locales (#26728)

app/javascript/styles/mastodon/forms.scss

@@ -1185,14 +1185,14 @@ code {
   }
 
   li:first-child .label {
-    left: auto;
     inset-inline-start: 0;
+    inset-inline-end: auto;
     text-align: start;
     transform: none;
   }
 
   li:last-child .label {
-    left: auto;
+    inset-inline-start: auto;
     inset-inline-end: 0;
     text-align: end;
     transform: none;