- Run TSAN jobs with +thread_sanitizer_cmm which enables Cmm
  instrumentation as well.
- Run TSAN jobs in deb12 which ships gcc-12, a reasonably recent gcc
  that @bgamari confirms he's using in #GHC:matrix.org. Ideally we
  should be using latest clang release for latest improvements in
  sanitizers, though that's left as future work.
- Mark TSAN jobs as manual+allow_failure in validate pipelines. The
  purpose is to demonstrate that we have indeed at least fixed
  building of TSAN mode in CI without blocking the patch to land, and
  once merged other people can begin playing with TSAN using their own
  dev setups and feature branches.