Add fallback CSS for WP 6.5

Author: t-hamano

src/admin/components/welcome-guide/style.scss

@@ -4,4 +4,9 @@
 	img {
 		margin-bottom: $grid-unit-20;
 	}
+
+	// Fallback for WP 6.5
+	.components-guide__footer {
+		box-sizing: border-box;
+	}
 }