Rollup merge of #148378 - ilai-deutel:update_hook-doc, r=joboet

Fix documentation for std::panic::update_hook

The equivalent code given in the documentation of `std::panic::update_hook`[^1] does not compile:

* `set_hook` expects a boxed function
* Missing closing delimiter for the closure

[^1]: rust-lang/rust#92649

Author: GuillaumeGomez