[9.18] Test secure chain that includes inactive KSK
requested to merge 4625-broken-trust-chain-on-corner-case-secure-chain-fixup-keytrap-test-only-v9_18 into bind-9.18
Partial Backport of MR !8848 (merged)
Add a regression test case for the scenario where a secure chain of trust includes an inactive KSK, that is a KSK that is not signing the DNSKEY RRset.
(cherry picked from commit f0bfd276)
Also see #4625 (closed)