DOC: Mention copy=True for __array__ method in the migration guide.

[charris]

Backport of #26097.

Addresses #25941 (comment)

Hi @ngoldbaum,

With this PR, explicit copy argument is always passed to __array__.
NPY_ARRAY_ENSURECOPY check was missing from flags processing, to cover all supported values for copy:

numpy/numpy/_core/src/multiarray/ctors.c

Lines 2417 to 2420 in 7f1c8cb

	* @param copy Specifies the copy behavior
	* NOTE: For copy == -1 it passes `op.__array__(copy=None)`,
	* for copy == 0, `op.__array__(copy=False)`, and
	* for copy == 1, `op.__array__(copy=True).

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