Rollup merge of #138353 - RalfJung:expose-provenance-must-use, r=ibraheemdev

remove must_use from <*const T>::expose_provenance

`<*mut T>::expose_provenance` does not have this attribute, and in fact the function is documented to have a side-effect, so there are perfectly legitimate use-cases where the return value would be ignored.

Author: fmease