Ensure current Python interpreter is used for subprocesses

[akx]

One spot used python, the other used python3 – sys.executable is known to be correct.

[akx]

How can the tests fail (in CI, not locally!) with

Traceback (most recent call last):
  File "/home/runner/work/LibCST/LibCST/libcst/codemod/tests/test_codemod_cli.py", line 23, in test_codemod_formatter_error_input
    sys.executable,
NameError: name 'sys' is not defined

when

LibCST/libcst/codemod/tests/test_codemod_cli.py

Lines 8 to 9 in 4e70f7b

	import subprocess
	import sys

[zsol]

Looks like you'll need to rebase this pr, it's based on a commit from 2020

[akx]

Looks like you'll need to rebase this pr, it's based on a commit from 2020

Note to self: check where your origin/master points at before branching off it.

[zsol]

To be fair, github doesn't exactly make this obvious

[zsol]

Thanks!