PEP-734 has been accepted (for 3.14).
(FTR, I'm opposed to putting this under the concurrent package, but
doing so is the SC condition under which the module can land in 3.14.)
The subinterpreter tests have data races (see gh-129824).
TSAN attempts to intercept some of the fatal signals, which can lead to
bogus reports. We could possibly handle these via TSAN_OPTIONS, but it's
simpler to just skip those tests -- they're not multithreaded anyways.
