Support mixed case model package names

[adrianeboyd]

Description

Support mixed case model package names

The current status seems to be:

• pip and setuptools support mixed case names, although case isn't significant in package names
• you can load a package with uppercase characters with spacy.load() or with a direct import
• spacy validate and the CI CLI tests fail on cases with uppercase characters

I don't see any evidence of the bug mentioned in 8dbe49e in tests with current versions of setuptools and pip.

Types of change

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Checklist

• I confirm that I have the right to submit this contribution under the project's MIT license.
• I ran the tests, and all new and existing tests passed.
• My changes don't require a change to the documentation, or if they do, I've added all required information.