docs: deprecation.rst: Add missing arguments to example code

[luziferius]

pytest/doc/en/deprecations.rst

Lines 241 to 247 in c27c8f4

	This form of test function doesn't support fixtures properly, and users should switch to ``pytest.mark.parametrize``:
	.. code-block:: python
	@pytest.mark.parametrize("x, y", [(2, 4), (3, 9)])
	def test_squared():
	assert x ** x == y

In the proposed new style using @pytest.mark.parametrize,
the example function signature missed the actual arguments.
Add the missing arguments.

[nicoddemus]

Thanks, appreciate it!