[CI] Disable spawn when running V1 Test

[tdoublep]

I noticed that V1 Test is failing on main branch ever since we merged: #14243

The error suggests that the monkeypatch that is used in test_engine_core_client does not get picked up when using spawn. It looks like this is a known issue with monkeypatch.

If we really need to use spawn for this test, a proper solution would be to re-write the test to not use monkeypatch. However, since this issue is actually failing all PR builds currently I would suggest reverting using spawn when running this test (since they seem to pass).

Have confirmed this reproduces locally and disabling spawn resolves it.

cc @russellb @youkaichao @aarnphm

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