bpo-43316:  gzip: CLI uses non-zero return code on error. (GH-24647)

Exit code is now 1 instead of 0. A message is printed to stderr instead of stdout. This is
the proper behaviour for a tool that can be used in scripts.
diff --git a/Lib/test/test_gzip.py b/Lib/test/test_gzip.py
index c3fa9b0..1bb8f7a 100644
--- a/Lib/test/test_gzip.py
+++ b/Lib/test/test_gzip.py
@@ -774,10 +774,10 @@ def test_decompress_infile_outfile(self):
         self.assertEqual(err, b'')
 
     def test_decompress_infile_outfile_error(self):
-        rc, out, err = assert_python_ok('-m', 'gzip', '-d', 'thisisatest.out')
-        self.assertIn(b"filename doesn't end in .gz:", out)
-        self.assertEqual(rc, 0)
-        self.assertEqual(err, b'')
+        rc, out, err = assert_python_failure('-m', 'gzip', '-d', 'thisisatest.out')
+        self.assertIn(b"filename doesn't end in .gz:", err)
+        self.assertEqual(rc, 1)
+        self.assertEqual(out, b'')
 
     @create_and_remove_directory(TEMPDIR)
     def test_compress_stdin_outfile(self):