Not sure if this is correct for this case but it looks like in the past an updated netboot image was provided which listed the updated version of libc6-udeb.
diff ubuntu/dists/focal/main/installer-amd64/current/legacy-images/udeb.list ubuntu/dists/focal-updates/main/installer-amd64/current/legacy-images/udeb.list |grep libc6-udeb < libc6-udeb 2.31-0ubuntu9 amd64 > libc6-udeb 2.31-0ubuntu9.2 amd64
Not sure if this is correct for this case but it looks like in the past an updated netboot image was provided which listed the updated version of libc6-udeb.
diff ubuntu/ dists/focal/ main/installer- amd64/current/ legacy- images/ udeb.list ubuntu/ dists/focal- updates/ main/installer- amd64/current/ legacy- images/ udeb.list |grep libc6-udeb
< libc6-udeb 2.31-0ubuntu9 amd64
> libc6-udeb 2.31-0ubuntu9.2 amd64