respdiff jobs do not need "allow_failure: true"

ASAN and TSAN respdiff jobs should be stable and not require allow_failure: true anymore.

All respdiff jobs passed in today's daily pipelines:

• main - https://gitlab.isc.org/isc-projects/bind9/-/pipelines/131269
• v9_18 - https://gitlab.isc.org/isc-projects/bind9/-/pipelines/131272
• v9_16 - https://gitlab.isc.org/isc-projects/bind9/-/pipelines/131274