Change scope of ndarray custom validators

[braingram]

As noted in a comment:

asdf/asdf/_core/_validators/ndarray.py

Lines 7 to 9 in 5e3983e

	# The validators in this module should really only be applied
	# to ndarray-* tags, but that will have to be a 3.0 change.
	tags = ["**"]

Prior to new-style extension custom validators the ndarray related validated applied to all tags. Scoping these to ndarray makes sense. This missed the 3.0 release and could be included in 4.0

[braingram]

Doh, duplicate of #1693