Fix static_mut_ref warning

[dtolnay]

New in nightly-2024-01-10 due to rust-lang/rust#117556.

warning: shared reference of mutable static is discouraged
   --> src/lib.rs:170:29
    |
170 |         let argv = unsafe { &ARGV };
    |                             ^^^^^ shared reference of mutable static
    |
    = note: for more information, see issue #114447 <https://github.com/rust-lang/rust/issues/114447>
    = note: reference of mutable static is a hard error from 2024 edition
    = note: mutable statics can be written to by multiple threads: aliasing violations or data races will cause undefined behavior
    = note: `#[warn(static_mut_ref)]` on by default
help: shared references are dangerous since if there's any kind of mutation of that static while the reference lives, that's UB; use `addr_of!` instead to create a raw pointer
    |
170 |         let argv = unsafe { addr_of!(ARGV) };
    |                             ~~~~~~~~~~~~~~