Fix test_gzip's failure under WASI, which does not have zlib, by using
test.support.import_helper.import_module to import zlib. (gzip
unconditionally imports zlib, so this does not cause any new skips.)
import struct
import sys
import unittest
-import zlib
from subprocess import PIPE, Popen
from test.support import import_helper
from test.support import os_helper
from test.support.script_helper import assert_python_ok, assert_python_failure
gzip = import_helper.import_module('gzip')
+zlib = import_helper.import_module('zlib')
data1 = b""" int length=DEFAULTALLOC, err = Z_OK;
PyObject *RetVal;