Code review comment for ~enr0n/+git/systemd-hwe:main

I believe I addressed all of your review comments. Of note, I went with the "follow systemd's version number" option. I think this is basically analogous to u-r-u's approach, but in that case following the Ubuntu release number makes sense.

Also, I added a check in tests/hwdb-redundancy for stderr output from `systemd-hwdb update`. IMO, this replicates the only functionality we would benefit from if we copied upstream's test/hwdb-test.sh.