Drop support for Python 3.7

[gruzewski]

Describe the bug/feature
In 3 months, Python 3.7 will stop receiving any new updates (more details here). I am trying to replace a deprecated package distutils.dir_util and to do that, I need a feature added in Python 3.8 (see #964). Do you know if there is anything that requires Python 3.7? Otherwise, I am happy to do the investigation.

To Reproduce
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Expected behavior
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Screenshots

Additional context
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