abi-check does not know which source is older, newer

We are not bumping the API version number compared to the reference version, so this results in abi-checker being unable to discern which version is "older" and which one is "newer". As a result, it uses git commit hashes to tell them apart. In case of https://gitlab.isc.org/isc-projects/bind9/-/jobs/814076 current HEAD of v9_16 to be treated as "old":

Report: compat_reports/libns/1601.0.0-2c0adf7e5a_to_1601.0.0-d497c325e7/compat_report.html

commit d497c325e70400f082bf59f61430e3f20a708d0d
Author: Tinderbox User <tbox@isc.org>
Date:   Wed Mar 11 16:35:45 2020 +0000

commit 2c0adf7e5abf1ad7932eb845e7dce9231e505d45
Merge: e11d690ae7 ad79e7c080
Author: Ondřej Surý <ondrej@isc.org>
Date:   Wed Apr 8 15:13:10 2020 +0000