Fix CI test configuration

[danieldaquino]

Tests pass but CI considers them a failure.

Example log:

# { total: 538, pass: 538 }
# time=37928.841ms
Error: Process completed with exit code 1.

[danieldaquino]

Found the root cause as I was working on some unrelated changes.

https://node-tap.org/coverage/#:~:text=For%20that%20reason%2C%20the%20tap%20runner%20instruments%20code%20using%20the%20builtin%20V8%20coverage%20API%2C%20and%20considers%20incomplete%20coverage%20to%20be%20atest%20failure:

For that reason, the tap runner instruments code using the built in V8 coverage API, and considers incomplete coverage to be a test failure.

I do not agree with the philosophy that tests need to have 100% line coverage to be useful. I will enable the --allow-incomplete-coverage flag on #24.