In SERVER-48280, we created a new build variant that runs tests with TSAN on Ubuntu 20.04. We knew from the outset that WT would very likely fail those tests, which is why we used Biggie to beghin with.

We specifically excluded tests tagged as requiring it in the build variant. However, unittests don't respect those tags. Exclude the entire WT directory in tsan.blacklist so the tests no longer fail.