fix: test: Allow TTL skew in the badcache print unit test

If the machine running the job is extra loaded (or extra slow), the
print test in the badcache unit test would fail because the TTL would be
59 (possibly even lower) and the test expects the badcache.out to only
have TTL 60.  Refactor the test to check for the expected strings and
check whether the TTL is in the expected range.

Closes #4861

Merge branch '4861-allow-TTL-skew-in-badcache_test' into 'main'

Closes #4861

See merge request isc-projects/bind9!9338