Allow Terraform check to run from Windows too
Summary:
From Cygwin, with a Python interpreter installed for Windows and not
as a Cygwin package, a POSIX sh script check works if #!/usr/bin/env sh,
but not with a #!/bin/sh shebang.
Even if Cygwin populates correctly sh in /bin directory.
References:
Test Plan:
Tested under Windows 11 25H2 (26200.9106), pre-commit 3.8.0
and Cygwin 3.6.10-1.x86_64.
Differential Revision: https://devcentral.nasqueron.org/D4163