Add py and pypy interpreters for Python

[lordmauve]

Add py, pypy and pypy3 interpreters for Python.

Description

This PR adds a few common interpreters that are missing for Python:

• py is https://github.com/brettcannon/python-launcher, which is modelled on PEP-397. In essence py is a Python community standard with specified behaviour. The implementation is not but it is offered by a Python core developer and steering council member.
• pypy and pypy3 refer to the PyPy Python JIT Interpreter, and are found in official downloads from https://www.pypy.org/download.html

The intention of this change is to enable Python syntax highlighting in scripts with shebangs such as

#!/opt/local/bin/py -3.11

or

#!/usr/bin/pypy3

Checklist:

• I am fixing a misclassified language
  • I have included a new sample for the misclassified language:
    • Sample source(s): I have examples in a GitHub Enterprise account that I cannot share
    • Sample license(s): Proprietary
  • I have included a change to the heuristics to distinguish my language from others using the same extension.

[lildude]

LGTM. Thanks.

Note: this PR will not be merged until close to when the next release is made. See here for more details.