venv/scripts/common/activate should use `uname` instead of `$OSTYPE` to detect Cygwin and MSYS

[J-M0]

Bug report

Bug description:

The venv activate script uses the $OSTYPE variable to determine if it's running on Cygwin or MSYS.

cpython/Lib/venv/scripts/common/activate

Lines 41 to 49 in fb202af

	# on Windows, a path can contain colons and backslashes and has to be converted:
	if [ "${OSTYPE:-}" = "cygwin" ] || [ "${OSTYPE:-}" = "msys" ] ; then
	# transform D:\path\to\venv to /d/path/to/venv on MSYS
	# and to /cygdrive/d/path/to/venv on Cygwin
	export VIRTUAL_ENV=$(cygpath "__VENV_DIR__")
	else
	# use the path as-is
	export VIRTUAL_ENV="__VENV_DIR__"
	fi

$OSTYPE is not defined by POSIX. It's provided by bash and zsh, but may not be present in other shells like dash. The uname command is always available in any shell and should be used instead.

CPython versions tested on:

3.12

Operating systems tested on:

Windows

Linked PRs

• gh-112507 Detect Cygwin and MSYS with uname instead of $OSTYPE #112508
• [3.12] gh-112507: Detect Cygwin and MSYS with uname instead of `$OS… #130674