ci: Check for copyright in Python scripts

[dougch]

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Problem:

The copyright_mistake_scanner.sh doesn't look at python scripts

Solution:

Update the S2N_FILES variable to look at *.py

• Does this change what S2N sends over the wire? no
• Does this change any public APIs? no
• Which versions of TLS will this impact? n/a

Requirements / Acceptance Criteria:

This will likely require a large PR to address.

Out of scope:

Is there anything the solution will intentionally NOT address?

[jmayclin]

Fixed in #4732