`change_ring` to non-field gives inconsistent result

[user202729]

We may have two modules M1 and M2 such that M1 == M2 but M1.change_ring(ZZ) != M2.change_ring(ZZ).

M1 = (QQ^2).span_of_basis([(1, 2)])
M2 = (QQ^2).span_of_basis([(2, 4)])
assert M1 == M2
assert M1.change_ring(ZZ) != M2.change_ring(ZZ)

Proposal: Something like M1.intersection(ZZ^2) appears to work at the moment. It might be a good idea to inform the user of the behavior of change_ring in its documentation, which might be unexpected, and point out alternatives.