`tests/wallet/test_wallet_subscription.py::test_wallet_subscription_mint` fails sometimes (but not always)

[aaronmcdaid]

Sometimes it fails with the following error:

# poetry run pytest tests/wallet/test_wallet_subscription.py::test_wallet_subscription_mint -v
=============== short test summary info =====================
FAILED tests/wallet/test_wallet_subscription.py::test_wallet_subscription_mint - AssertionError: assert 5 == 3
=============== 1 failed, 1 warning in 6.14s

Sometimes, it's 4 == 3 instead of 5 == 3, and sometimes it passes

It's line 54 of tests/wallet/test_wallet_subscription.py:

    assert len(msg_stack) == 3