Center the text itself in upload area (#24029)

app/javascript/styles/mastodon/components.scss

@@ -4407,6 +4407,7 @@ a.status-card.compact:hover {
   display: flex;
   align-items: center;
   justify-content: center;
+  text-align: center;
   color: $secondary-text-color;
   font-size: 18px;
   font-weight: 500;