Update `bindgen` dependency

[kkysen]

bindgen currently generates layout tests that invoke UB, specifically nullptr derefs (see rust-lang/rust-bindgen#1651). These are warned by rustc and may be errors soon. A fix (rust-lang/rust-bindgen#2203 on 5/17/2022) has already been merged, but hasn't landed in a release yet. So we should update our bindgen dependencies as soon as a new release lands.

[fw-immunant]

Bindgen 0.60.1 just came out; I'll bump our dep prior to our pending 0.16.1 release.

[kkysen]

Great! I just checked; 0.60 fixes the issue.