The ARTIFACTS_SUFFIX is being dropped on building scripts because:

1) This will make possible to further simplify Installer scripts in other commit

2) There is no script that uses multi-arch _build/_install at same time on CI
   However, there are two use cases: to build Debian and flatpak; and, on Win,
   to build on CLANGARM64 and CLANG64 (?). But probably they are pretty niche.
   I suppose that people who build on Debian (or other dev-oriented distro)
   willn't want to mantain deps in two sys prefixes (pkg and GNOME runtime)
   + two gimp prefixes (out of sandbox and sandbox) due to huge storage use.
   Why someone would want to build with emulation on Win ARM64 I don't know.
   Anyway, people that know how to do this stuff probably can change the .sh.

3) When building locally, the contributor doesn't need to know the arch at all.
   Indeed, without this suffix, the scripts are inline with gimp-web-devel and
   prevent some first-sight confusion when reading them that I've seen on IRC.

4) These arch suffixes can be understood as '_install-*' being distributable
   which is not true. So, without this suffix we could make more clear
   what is a package (when GitLab fix the glob bug in 'expose_as' someday).

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Despite .gitlab-ci.yml not being a script, it needed to be touched too
because cross scripts depends on Debian jobs due to gimp-data MR.