Add a TSAN suppression for leveldb

Summary: The leveldb test leak thread. It is hard to fix due to design choices in leveldb, and it is not a significant problem anyways.

Test Plan:

ninja check-leveldb

Using tsan.

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D8709