[CVE-2020-8625] [CVE-2021-25216] Add a tool for reproducing ISC SPNEGO bugs

Extend the "tsiggss" system test with reproducers for CVE-2020-8625 and CVE-2021-25216.

NOTE: This MR cannot be merged at the moment (see a discussion elsewhere for context) - it needs to wait until ASAN-enabled CI jobs are moved to Fedora 38, which is expected to happen around May 2023.

Moved from isc-private/bind9!287

Closes #2354 (closed)