Disable allow_failure for ThreadSanitizer jobs

Since the main branch is now TSAN-clean, it's a good opportunity to
enable hard failures for the TSAN system test jobs.

.gitlab-ci.yml

@@ -334,7 +334,6 @@ stages:
 
 .system_test_tsan: &system_test_tsan_job
   <<: *system_test_common
-  allow_failure: true
   after_script:
     - cat bin/tests/system/test-suite.log
     - find bin -name 'tsan.*' -exec python3 util/parse_tsan.py {} \;