ci: Use `meson introspect` to generate artifact path

ci: Use `meson introspect` to generate artifact path

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/gnome-shell/-/merge_requests/3340>
(cherry picked from commit 27445a1c98a463bcb826edae9850972c3616b90c)