Prompted by #29705
Note that x-systemd.wanted-by= and x-systemd.required-by= are not
dropped, since we ignore them because they are unnecessary rather
than unapplicable.
It is marked and named as a script, so add +x otherwise Lintian complains:
W: systemd-tests: script-not-executable [usr/lib/systemd/tests/testdata/units/generator-utils.sh]