fix justify-self (#4723)

blockbase/assets/ponyfill.css

@@ -709,7 +709,7 @@ div.wp-block-query-pagination .wp-block-query-pagination-previous {
 }
 
 div.wp-block-query-pagination .wp-block-query-pagination-next {
-	justify-self: end;
+	justify-self: flex-end;
 	grid-area: next;
 }
 

blockbase/sass/blocks/_query-pagination.scss

@@ -16,7 +16,7 @@ div.wp-block-query-pagination { // This CSS needs to be stronger than Gutenberg'
 	}
 
 	.wp-block-query-pagination-next {
-		justify-self: end;
+		justify-self: flex-end;
 		grid-area: next;
 	}