Use coverage in the CI

[moi15moi]

I think it would be beneficial to use coverage to track which part of comtypes is covered by tests.

The report created by coverage could be published on codecov.io.
In our CI, we could create the report and use codecov/codecov-action to publish it.

Here is a example of a project on codecov.io: https://app.codecov.io/github/moi15moi/FontCollector
As you can see, you can clearly see which part is covered and which part isn't which helps a lot to create some tests.

Note that I am note sure if it will properly detect the code covered in the server, but I still think it would be a plus.

[junkmd]

That's a great idea!

First, I’d appreciate it if you could test and verify what the appropriate codecov.io configuration for this project would be within your forked repository.

If applying codecov.io requires repository owner permissions, please let me know. I’m considering reaching out to Enthought, the host of this repository, to either allocate the necessary permissions or make the required configuration changes.

[moi15moi]

Just so you know, this issue is currently blocked by this bug: nedbat/coveragepy#1920