Use new contract in test_declare_v3_tx

[ddoktorski]

Towards #1698

• This test fails when running on a single thread as the same contract is already declared in other test. We should have more sophisticated solution for example with salting instead of adding new contracts that are basically the same, but for now this is the easiest fix

[ddoktorski]

This change is part of the following stack:

• Add explicit package in load_contract calls #1718
  • Stop using sys.args logic in test #1719
    • Use new contract in test_declare_v3_tx #1720 ◀
      • Fix Windows CI tests #1721
        • Bump devnet to v0.8.1 #1722

_{Change managed by git-spice.}