Add markers for tests requiring network connection

[mcepl]

All Linux distributions (and I guess some CIs as well) block any network connections to the isolated environments. Would it be possible to add pytest marker marking all test cases requiring network access (currently, it is only test_get_changelog_url)? Thank you.

Possible patch for the current tarball

[orsinium]

Wow, a patch, so old-school. Could you make a PR, please? :)

UPD: I can apply the patch but I'd like to preserve the attributions.

[mcepl]

I am sorry, I am maintainer of all Python packages in openSUSE. I really cannot fork and maintain forks for all thousand or so of them. I don’t care about the attribution (it is "Matěj Cepl <mcepl at cepl dot eu>" if you care), you can apply it with your credentials if you wish.