Fix coveralls error on GitHub Actions
Fix coveralls error on GitHub Actions

Coveralls started failing suddenly in GitHub Actions Worflows.
This feels like a bug on their side (at least their documentation)
because the `CI` environment variable is not supposed to be set refs:
https://help.github.com/en/actions/configuring-and-managing-workflows/using-environment-variables#default-environment-variables
Disabling the `coveralls` conditional run from the `Makefile` fixes it.
It wasn't needed as Travis already calls it explicitly without going
through the `test` target.
Error was:
```
/bin/sh: 1: .tox/py36/bin/coveralls: not found
Makefile:30: recipe for target 'test' failed
make: *** [test] Error 127
```

PKRoma/python-for-android,kronenpj/python-for-android,germn/python-for-android,kivy/python-for-android,germn/python-for-android,kronenpj/python-for-android,kivy/python-for-android,germn/python-for-android,kronenpj/python-for-android,germn/python-for-android,rnixx/python-for-android,kronenpj/python-for-android,PKRoma/python-for-android,rnixx/python-for-android,PKRoma/python-for-android,rnixx/python-for-android,rnixx/python-for-android,PKRoma/python-for-android,kronenpj/python-for-android,kivy/python-for-android,germn/python-for-android,kivy/python-for-android,rnixx/python-for-android,PKRoma/python-for-android,rnixx/python-for-android,kivy/python-for-android,germn/python-for-android