CI: setup-msys2 2.5.0
Upstream has released setup-msys2 2.5.0. We should check if it would provide more sensible environment to use than the 2.4.2 we currently use.
They still use the same msys2 snapshot as in 2.4.2, so this update does not help us to get rid of the hacks from installer_msys2/Makefile. Still, we probably want to be up-to-date with setup-msys2.
Upstream has released setup-msys2 2.5.0. We should check if it would provide more sensible environment to use than the 2.4.2 we currently use.