Ensure suffix is always valid in bin/tests/system/qmin/ans4/ans.py (CID 350722)

Coverity CID 350722:

170        r.answer.append(
171            dns.rrset.from_text(
172                lqname + suffix, 1, IN, NS, "a.bit.longer.ns.name." + suffix
173            )
174        )
175        r.flags |= dns.flags.AA
    15. Condition endswith(lqname, "icky.ptang.zoop.boing."), taking true branch.
176    elif endswith(lqname, "icky.ptang.zoop.boing."):

CID 350722 (#7 of 7): Bad use of null-like value (FORWARD_NULL)
16. invalid_operation: Invalid operation on null-like value suffix.
177        r.authority.append(
178            dns.rrset.from_text(
179                "icky.ptang.zoop.boing." + suffix,
180                1,
181                IN,
182                SOA,
183                "ns2." + suffix + " hostmaster.arpa. 2018050100 1 1 1 1",
184            )
185        )