fix installation of easybuild-easyconfigs with setuptools>=61 by explicitly declaring there are no Python packages

[branfosj]

fixes #790

Tested with:

$ python3 -m venv
$ source venv/bin/activate
$ cd easybuild-framework/
$ pip install .
$ cd ../easybuild-easyblocks/
$ pip install .
$ cd ../easybuild-easyconfigs/
$ pip install .

And $ eb --search pytorch shows expected output.

Two tests with:

• updating setuptools to latest (61.2.0)
• using EB installed Python 3.9.5, which has 56.0.0
• using OS Python 3.6.8 which has 39.2.0

[branfosj]

We might want to add a test install github action - for several python versions:

• update setuptools and pip
• install framework develop
• install blocks develop
• install easyconfigs PR

The downside of such testing is that it will cause a failure of PRs that is unrelated to the contents of the PR.

[boegel]

@branfosj We could test this in a separate workflow, that runs daily (rather than running it on PRs)

[boegel]

I compared the source tarball that's created with python3 setup.py sdist with and without this change (using setuptools 57.4.0), they're identical (other than the setup.py itself), so good to go...

Thanks @branfosj!

[akesandgren]

Does this solve easybuilders/easybuild-framework#3984 too?

[boegel]

@akesandgren Yes, it should indeed.