Mark test that require access to the internet

[avalentino]

Description Of Changes

I some cases it is necessary to run teh test suite in an environment without access to teh internet (e.g. when one is building Debian packages).

This PR add the "network" mark to all tests requiring access to the internet.

In this way, it is easy to skip them using the following command:

$ python3 -m pytest -m "not network" tests

Checklist

• Closes #xxxx
• Tests added
• Fully documented

[dopplershift]

@avalentino I assume this is building from the sdist on PyPI and not from a git checkout? Looks like network access comes from downloading our testdata. I wonder if it's worth finding a way to distribute the testdata instead?

[avalentino]

Yes in debian we use source tarball coming from the git tag, not the pypi sdist.
Honestly I didn't check if there is any difference in contents.
Yes in almost all the cases the access to the interned is done for getting data.
There are also 4 tests in which the access to the interned is done via cartopy to download base maps I guess.

To me having the test marked in some way is still a good thing, even if you decide to distribute the test data.

[avalentino]

... of course the mark name could be different if you prefer e.g. "remotedata" or "pooch"