Fix typo in Word::get_by_id docs (bevyengine#5246)

I believe this should read `immutable` not `mutable`



Co-authored-by: Obdzen <108854527+Obdzen@users.noreply.github.com>

crates/bevy_ecs/src/world/mod.rs

@@ -1468,7 +1468,7 @@ impl World {
         Some(())
     }
 
-    /// Retrieves a mutable untyped reference to the given `entity`'s [Component] of the given [`ComponentId`].
+    /// Retrieves an immutable untyped reference to the given `entity`'s [Component] of the given [`ComponentId`].
     /// Returns [None] if the `entity` does not have a [Component] of the given type.
     ///
     /// **You should prefer to use the typed API [`World::get_mut`] where possible and only