Bump Rust to nightly-2025-09-21 (#83415)
It compiles fine, but we have another problem: `cargo fmt` really doesn't like it
```
cargo fmt -- turbopack/crates/turbo-tasks-fs/src/lib.rs
error: let chains are only allowed in Rust 2024 or later
--> /Users/niklas/code/next.js/turbopack/crates/turbo-tasks-fs/src/lib.rs:749:44
|
749 | if create_directory && let Some(parent) = full_path.parent() {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: let chains are only allowed in Rust 2024 or later
--> /Users/niklas/code/next.js/turbopack/crates/turbo-tasks-fs/src/lib.rs:893:44
|
893 | if create_directory && let Some(parent) = full_path.parent() {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: let chains are only allowed in Rust 2024 or later
--> /Users/niklas/code/next.js/turbopack/crates/turbo-tasks-fs/src/lib.rs:1233:12
|
1233 | if let Some(path) = join_path(&self.path, path)
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
```
The precommit hook that selectively runs on files is simply not a supported usecase.
So I changed that to `rustfmt --edition 2024 -- ` now :shrug:
Previous discussion: https://vercel.slack.com/archives/C03EWR7LGEN/p1748898285716779
