Workaround problem with node not closed correctly

Pytest has a bug, which interrupts test teardown, when warning is emitted. This bug is visible only, when warnings are treated as errors. So I turned off treating warnings as errors, wrote issue on Pytest repo. When problem will be fixed, I will revert this commit.

Issue in pytest repo: https://github.com/pytest-dev/pytest/issues/9670

Corresponding merge request in TestTools: test-tools!34 (merged)