fix(task): add missing which dep on Windows

The `.cmd`→`.ps1` rewrite moved from `vite_task_plan` (where `which`
was already a dep) to `vite_task` without bringing the dep along.
Windows CI failed with E0433. Only needed at `cfg(windows)`.

Author: fengmk2

crates/vite_task/Cargo.toml

@@ -49,6 +49,7 @@ tempfile = { workspace = true }
 nix = { workspace = true }
 
 [target.'cfg(windows)'.dependencies]
+which = { workspace = true }
 winapi = { workspace = true, features = ["handleapi", "jobapi2", "winnt"] }
 
 [lib]