Patchtest tries to apply the received patch on the repository, without
specifying the directory, which means that the CWD is used. In case the
patch modifies a content in a different folder (e.g. the script is running
in ./meta, but the patch modifies ./meta-selftest), the patch will be skipped,
but git still returns 0, instead of complaining.
To avoid such false positives, specify the working directory for applying the
patch - the top of the repodir.