Fixed #29154 -- Corrected examples in pluralize template filter docstring and added tests.

[hramezani]

Fix pluralize template filter and add some tests.

[timgraham]

Use meaningful test names, e.g. test_no_arguments.

Also I would have 3 tests and use a loop a subTest() to test the three cases for each template. For example:

tests = (('0', 'votes'), ...)
for value, expected in tests:
    with self.subTest(value=value):
        output = self.engine.render_to_string('pluralize01', {'value': value})
        self.assertEqual(output, expected)

[hramezani]

@timgraham thanks, requested changes done