Future compile error on Rust beta 1.60 in types/tests.rs

[the8472]

A crater run found that this crate's tests no longer compile with rust 1.60 beta (see rust-lang/rust#94504) due to a newly added method causing conflicts in method resolution.

The regression has been deemed an acceptable minor change per RFC 1105.
It can be fixed by using fully qualified function call syntax to unambiguously call the extension trait that previously provided abs_diff or by switching to the new std API once 1.60 is released.