Update test compat with pyftpdlib>=1.5.10

[mweinelt]

Type of changes

• Bug fix

Checklist

• I've run the latest black with default args on new code.
• I've updated CHANGELOG.md and CONTRIBUTORS.md where appropriate.
• I've added tests for new code.
• I accept that @PyFilesystem/maintainers may be pedantic in the code review.

Description

The pyftpdlib library in version 1.5.10 renamed the ThreadedTestFTPd to FtpdThreadWrapper. I've updated that reference and ran the tests. I also updated the version requirement to my best knowledge.

[musicinmybrain]

This seems to be on the right track, but doesn’t seem quite right at the moment. It looks like pyftpdlib 1.5.10 still has ThreadedTestFTPd, and FtpdThreadWrapper was introduced in pyftpdlib 2.0.

https://github.com/giampaolo/pyftpdlib/blob/3cea779de3ccb5ab5744220de3bddb3d4ff10f35/pyftpdlib/test/__init__.py#L445

Also, there is another use of ThreadedTestFTPd in TestAnonFTPFS that needs to be adjusted:

pyfilesystem2/tests/test_ftpfs.py

Lines 331 to 347 in 77a8562

	@mark.slow
	@unittest.skipIf(platform.python_implementation() == "PyPy", "ftp unreliable with PyPy")
	class TestAnonFTPFS(FSTestCases, unittest.TestCase):
	user = "anonymous"
	pasw = ""
	@classmethod
	def setUpClass(cls):
	from pyftpdlib.test import ThreadedTestFTPd
	super(TestAnonFTPFS, cls).setUpClass()
	cls._temp_dir = tempfile.mkdtemp("ftpfs2tests")
	cls._temp_path = os.path.join(cls._temp_dir, text_type(uuid.uuid4()))
	os.mkdir(cls._temp_path)
	cls.server = ThreadedTestFTPd()

I used this PR as inspiration for #595.

[mweinelt]

Back then I applied a substitution downstream, so in practice I arrived at the same result as #595, and missed that it touched two tests. Thanks!