bpo-33455: Pass os.environ in test_posix::test_specify_environment. (GH-6753)

Pass os.environ's copy to new process created at test_posix:
test_specify_environment. Otherwise important variables such as
LD_LIBRARY_PATH are not set and the child process might not work at all
in an environment where such variables are required for Python to function.
(cherry picked from commit 7ec8f28)

Co-authored-by: Miro Hrončok <[email protected]>

Author: miss-islington

Lib/test/test_posix.py

@@ -1462,7 +1462,7 @@ def test_specify_environment(self):
         """
         pid = posix.posix_spawn(sys.executable,
                                 [sys.executable, '-c', script],
-                                {'foo': 'bar'})
+                                {**os.environ, 'foo': 'bar'})
         self.assertEqual(os.waitpid(pid, 0), (pid, 0))
         with open(envfile) as f:
             self.assertEqual(f.read(), 'bar')