Migrate to OpenZeppelin test environment

[nkuba]

We should update tests to OpenZeppelin test environment just like we did in keep-core (threshold-network/keep-core#1528) and keep-ecdsa (keep-network/keep-ecdsa#501).

References:

• Migrate to Openzeppelin test Environment threshold-network/keep-core#1533
• Migrate to OpenZeppelin test environment keep-ecdsa#501