Do not chdir to the parent directory in the CI

In the past, using the parent directory as the working directory has been
a source of troubles in the CI: since it does not get cleaned up on
runners that process multiple jobs (as the lightweight one does) stale
files from other jobs have been a source of failures.

The previous commits have switched the update script to use `$TMPDIR` as
the working directory anyway, but to be extra sure let's not `cd ..`
before invoking the script.

Signed-off-by: Emanuele Aina <emanuele.aina@collabora.com>