Use monkeypatch

[radarhere]

This PR uses monkeypatch rather than the current behaviour of setting and restoring sys.stdout.

Pillow/Tests/test_file_png.py

Lines 776 to 789 in d008d12

	old_stdout = sys.stdout
	class MyStdOut:
	buffer = BytesIO()
	mystdout: MyStdOut | BytesIO = MyStdOut() if buffer else BytesIO()
	sys.stdout = mystdout
	with Image.open(TEST_PNG_FILE) as im:
	im.save(sys.stdout, "PNG")
	# Reset stdout
	sys.stdout = old_stdout