Exclude tests in setup.py

[aldenrogers]

Proposed changes

This fixes #507 by specifying in setup.py that tests should not be packaged.

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Further comments

Compare https://github.com/quiltdata/quilt/pull/2632/files for an example of a similar change elsewhere.

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[aldenrogers]

I'll need some time to confirm with my employer before signing the CLA

[jeongyoonlee]

LGTM. Thanks for the contribution!