Turned out that the tiff-5 -> tiff-6 update has taken place only between the 221216 upstream snapshot, and our own 221223 snapshot. Thus setup-msys2 update that makes it to use 221216 is not enough to get rid of handling of tiff-5/tiff-6 difference between CI and regular msys2 builds.
Upstream has released setup-msys2-2.15.1 (and 2.15.0 before that).