build: exclude test folder from package build

[iloveitaly]

Without this the tests/ folder is included, which will shadow a local tests/ directory.

[Jakeroid]

@iloveitaly

Thank you! Do you mean the build still has test because of this missing line?

[Jakeroid]

@iloveitaly Thank you for your contribution!

[Jakeroid]

UPD: I was wrong. It works.

Previous Comment:

It turned out that CI would not work in this case.

We already exclude tests from the installation by having this packages=find_packages(exclude=['tests']) in the setup.py.
As for package at this point we can't do that. Maybe later on when the library will be migrate to modern package system it could be possible.

I will put changes back.