[Cashtab] update "Migrate legacy wallet on testnet" unit test

Summary:
The existing "Migrate legacy wallet on testnet" unit test is using mainnet addresses for
Path145 and Path245. This diff update it to use the testnet addresses as it should be

Test Plan:
cd web/cashtab
npm test
make sure all tests passed

Reviewers: bytesofman, #bitcoin_abc

Reviewed By: bytesofman, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D10612