`lib/dns/tests/dnstap_test.c` appears to be broken - it crashes on every run

The following discussion from !1744 (merged) should be addressed:

• @michal started a discussion:

  I verified that the changes from this branch compile fine in my environment and do not prevent dnstap from working.

  However, lib/dns/tests/dnstap_test.c appears to be broken - it crashes on every run. I suspect its cmocka rework is the root cause. Interestingly enough, we do not test --enable-dnstap in CI, even though we produce packages with dnstap support.

  Since these problems were not introduced by this branch, I am obviously okay with resolving this discussion by opening separate issues.