rust: list: Fix typo much in arc.rs

Correct the typo (s/much/must) in the ListArc documentation.

Reported-by: Miguel Ojeda <ojeda@kernel.org>
Closes: Rust-for-Linux#1166
Fixes: a480263 ("rust: list: add tracking for ListArc")
Signed-off-by: Sylvan Smit <sylvan@sylvansmit.com>
Reviewed-by: Benno Lossin <lossin@kernel.org>
Link: https://lore.kernel.org/r/20250529162923.434978-1-sylvan@sylvansmit.com
[ Changed tag to "Reported-by" and sorted. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: Sylvan Smit

rust/kernel/list/arc.rs

@@ -74,7 +74,7 @@ pub unsafe trait TryNewListArc<const ID: u64 = 0>: ListArcSafe<ID> {
 ///
 /// * The `untracked` strategy does not actually keep track of whether a [`ListArc`] exists. When
 ///   using this strategy, the only way to create a [`ListArc`] is using a [`UniqueArc`].
-/// * The `tracked_by` strategy defers the tracking to a field of the struct. The user much specify
+/// * The `tracked_by` strategy defers the tracking to a field of the struct. The user must specify
 ///   which field to defer the tracking to. The field must implement [`ListArcSafe`]. If the field
 ///   implements [`TryNewListArc`], then the type will also implement [`TryNewListArc`].
 ///