att/ast on Github has branched ksh2020 and reverted mainline back to
ksh93u+ and v-. See github commit 0be82553e98be77238577bc0eaafda0f1cf807fe.

To learn how and why our att/ast upstream made this decision see
https://github.com/att/ast/issues/1464 and
https://github.com/att/ast/issues/1466.

The next steps will be to update shells/ksh93-devel to att/ast master.
shells/ksh93 will likely be based on att/ast master at
0be82553e98be77238577bc0eaafda0f1cf807fe or some future tag or branch.