Adjust number of cores used by CI
Adjust number of cores used by CI

In the same way as in Travis, when python runs inside Cirrus CI, pytest-xdist
`-n auto` doesn't calculate the number of cores properly.

This commit changes the number of parallel process to 5, which should be
roughly equivalent to 2 * N + 1 for the most of the Cirrus CI environments.

blue-yonder/pyscaffold,blue-yonder/pyscaffold