const_trait_impl with associated types broken by effects, but now requires effects to be used in const fn

[maurer]

In current beta and beyond, #![feature(effects)] is required to use const_trait_impl in const fn contexts - #114808 .

However, turning on #![feature(effects)] with an output type on the trait yields an error about 'host' not being equal to 'true'

Without #![feature(effects)], this works on rust compilers 1.72 and earlier if unstable features are enabled.

[maurer]

The example is wrong and in fact shouldn't work (since it doesn't refer to a ~const bound). This was an attempt to reduce rust/kernel/driver.rs's IdArray::new to a code example, and I didn't do it right. Closing until I have a cleaner reproducer.