Comment 5 for bug 1791010

Essentially 4 LXD containers doing:
$ pull-lp-source mysql-5.7
$ apt build-dep mysql-5.7
$ sudo ./debian/rules clean && sudo ./debian/rules build

Sys-Bionic-SRC-Bionic: ok
Sys-Bionic-SRC-Cosmic: ok
Sys-Cosmic-SRC-Bionic: fail
Sys-Cosmic-SRC-Cosmic: fail

So it is one of the build dependencies, and not the mysql upgrade itself.
Very likely the same would also hit the former mysql that already is in -proposed (not worth to try wasting CPU power).

I think I need to bisect "apt upgrade" oO