We currently assume that the `CI_COMMIT_TAG` variable matches the
version component of the generated dist tarball.
That is usually correct, but sometimes errors happen and a wrong
tag is pushed, and the real release uses something like "46.0-real".
Account for that by building the artifact path from `meson introspect`
and exporting it as environment variable.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3775>
(cherry picked from commit bcfbc7fa17)
