Auto merge of #124636 - tbu-:pr_env_unsafe, r=petrochenkov

Make `std::env::{set_var, remove_var}` unsafe in edition 2024

Allow calling these functions without `unsafe` blocks in editions up until 2021, but don't trigger the `unused_unsafe` lint for `unsafe` blocks containing these functions.

Fixes #27970.
Fixes #90308.
CC #124866.

Author: bors