feat: Add support for Python 3.10

[adamchainz]

This necessitated an upgrade of pytest and pytest-xdist. I think they were probably only pinned for Python 2 compat.

[coveralls]

Pull Request Test Coverage Report for Build 1824832454

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 93.586%

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Totals
Change from base Build 1824261162:	0.0%
Covered Lines:	3254
Relevant Lines:	3477

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💛 - Coveralls

[adamchainz]

Fixed errors from pytest fixtures being called directly. docs, message (for many tests):

____ ERROR at setup of test_query_with_value_based_filters[20-0-file-None] _____
Fixture "search_entries" called directly. Fixtures are not meant to be called directly,
but are created automatically when test functions request them as parameters.
See docs.pytest.org/en/stable/explanation/fixtures.html for more information about fixtures, and
docs.pytest.org/en/stable/deprecations.html#calling-fixtures-directly about how to update your code.

[lukaszsocha2]

Thanks for contributing ! Actually the same task was in our roadmap for the next week, but you were faster than us ;) Just one comment to not specify lower limit of pytest library version and we're good to merge it.

[adamchainz]

Thanks for contributing ! Actually the same task was in our roadmap for the next week, but you were faster than us ;) Just one comment to not specify lower limit of pytest library version and we're good to merge it.

It's okay, I had to take a look as I was upgrading a client codebase to Python 3.10 and wanted to be sure Box wouldn't be a risk.

[adamchainz]

Great, cheers.

[arjankowski]

Thank you @adamchainz for your help 👍