Fix typo in the description of the `id` method in `ui.rs` (#7457)

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The description of the id method in the Ui struct incorrectly wrote
"where" instead of "were".

<img width="668" height="201" alt="Screenshot 2025-08-15 at 7 03 27 pm"
src="https://github.com/user-attachments/assets/df35cdab-b3ad-44d4-a565-cd9a4d883f21"
/>

This PR fixes that typo.

crates/egui/src/ui.rs

@@ -377,7 +377,7 @@ impl Ui {
     ///
     /// However, it is not necessarily globally unique.
     /// For instance, sibling `Ui`s share the same [`Self::id`]
-    /// unless they where explicitly given different id salts using
+    /// unless they were explicitly given different id salts using
     /// [`UiBuilder::id_salt`].
     #[inline]
     pub fn id(&self) -> Id {