update MSRV to 1.80 due to LazyLock

[romanstingler]

https://doc.rust-lang.org/std/sync/struct.LazyLock.html

warning: current MSRV (Minimum Supported Rust Version) is `1.78.0` but this item is stable since `1.80.0`
  --> src/exec.rs:28:52
   |
28 | static CAUGHT_SIGNAL: LazyLock<Arc<AtomicUsize>> = LazyLock::new(|| {
   |                                                    ^^^^^^^^^^^^^
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#incompatible_msrv

sorry already need to update that