gitlab-ci: Place files from the Mesa repo into the build tarball

gitlab-ci: Place files from the Mesa repo into the build tarball

There's some files from the .gitlab-ci directory that are needed in the
test stage and that, because the Mesa repository isn't checked out in
that stage, need to be made available through other means.

Because those files are going to be needed in LAVA devices, place them
ino the tarball containing the built files so it's available to both
gitlab-ci runners and LAVA devices.

Before those files were passed in the artifacts of the Gitlab CI job,
but this commit places them into the built tarball so scripts later in
the pipeline don't need to account for this discrepancy.

Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4295>