gh-90473: Misc test fixes for WASI (GH-93218)

* ``sys.executable`` is not set
* WASI does not support subprocess
* ``pwd`` module is not available
* WASI checks ``open`` syscall flags more strict, needs r, w, rw flag.
* ``umask`` is not available
* ``/dev/null`` may not be accessible
(cherry picked from commit 1f134e96ba)

Co-authored-by: Christian Heimes <christian@python.org>

Lib/test/test_netrc.py

@@ -1,6 +1,11 @@
 import netrc, os, unittest, sys, textwrap
 from test.support import os_helper, run_unittest
 
+try:
+    import pwd
+except ImportError:
+    pwd = None
+
 temp_filename = os_helper.TESTFN
 
 class NetrcTestCase(unittest.TestCase):
@@ -266,6 +271,7 @@ class NetrcTestCase(unittest.TestCase):
 
 
     @unittest.skipUnless(os.name == 'posix', 'POSIX only test')
+    @unittest.skipIf(pwd is None, 'security check requires pwd module')
     def test_security(self):
         # This test is incomplete since we are normally not run as root and
         # therefore can't test the file ownership being wrong.