Update test-warp-transfer.ts

[bap2pecs]

I was testing warp route and I got:

$ yarn ts-node scripts/test-warp-transfer.ts \ 
  --origin mumbai --destination snapchain --wei 123 \
  --recipient 0x9DA155Af6926eBbb72Bce91fD84efE8fC867274c \
  --key <REDACTED>


...
hyperlane:ERROR Error running Warp transfer test Error: missing provider (operation="call", code=UNSUPPORTED_OPERATION, version=abstract-signer/5.7.0)

after discussing with @nambrot offline, this is the suggested fix