gh-117657: Quiet erroneous TSAN reports of data races in `_PySeqLock` (#117955)

Quiet erroneous TSAN reports of data races in `_PySeqLock`

TSAN reports a couple of data races between the compare/exchange in
`_PySeqLock_LockWrite` and the non-atomic loads in `_PySeqLock_{Abandon,Unlock}Write`.
This is another instance of TSAN incorrectly modeling failed compare/exchange
as a write instead of a load.