Remove explicit semaphore in tests

Due to a recent switch to `hspec` from `tasty` we no longer need to create an explicit lock in tests, since `hspec` supports sequential test execution.
This task is about removing this ugly locking mechanism from `cardano-crypto-class` test suite:

https://github.com/IntersectMBO/cardano-base/blob/245d69de6dfd33105ef98e0e6d5efb41dc58c37f/cardano-crypto-class/test/Main.hs#L23-L27