Update next.md

Author: sylvestre

next.md

@@ -29,3 +29,4 @@ This file documents the pending improvements or regression:
 * https://github.com/uutils/coreutils/pull/6861
 * https://github.com/uutils/coreutils/pull/6885
 * https://github.com/uutils/coreutils/pull/5788
+* https://github.com/uutils/coreutils/pull/6621/