beta regression: postgis "the trait bound ... is not satisfied"

[alexcrichton]

Discovered by crater:

$ git clone https://github.com/andelf/rust-postgis
$ cd rust-postgis
$ cargo +beta test

cc @rust-lang/compiler, cc @andelf, @pka

[Mark-Simulacrum]

Should be fixed by #56003, and this issue is a duplicate of #54467; closing.