TYP: fix incorrect import in ma/extras.pyi stub

The `numpy.ma` tests for type stubs are missing, so this kind
of obvious error has a chance of creeping in. The import in the
type stub now matches the one in the corresponding .py file again.

Also add the start of a very basic "pass" typing test for numpy.ma

[skip azp] [skip cirrus] [skip circle]

Author: rgommers

numpy/ma/extras.pyi

@@ -1,5 +1,6 @@
 from typing import Any
-from numpy.lib.index_tricks import AxisConcatenator
+
+from numpy.lib._index_tricks_impl import AxisConcatenator
 
 from numpy.ma.core import (
     dot as dot,

numpy/typing/tests/data/pass/ma.py

@@ -0,0 +1,8 @@
+from typing import Any
+
+import numpy as np
+import numpy.ma
+
+
+m : np.ma.MaskedArray[Any, np.dtype[np.float64]] = np.ma.masked_array([1.5, 2, 3], mask=[True, False, True])
+