Fix Kraken testGettingMinOrderVolumeIfAvailable() unit test

[gazbert]

The test makes an actual call to the exchange to get the values used in the test assertions - too brittle!

Test to fix:
https://github.com/gazbert/bxbot/blob/3733bcb187c29365f74d6621f2ce2dbc287fddee/bxbot-exchanges/src/test/java/com/gazbert/bxbot/exchanges/TestKrakenExchangeAdapter.java#L1105C15-L1105C51

Patched:
f9a2a4a#diff-e4b2fe7ddebc9096854b04778f49ad546020a701b4a6268d000c2f40bdcd6e70

Change test so that it mocks out the network call.