Fix possessive "its" in docs and comments (#3998)

This PR fixes a number of places where we were incorrectly using "it's"
where we needed to use the possessive "its".

Release Notes:

- N/A

crates/ui/src/components/checkbox.rs

@@ -73,7 +73,7 @@ impl RenderOnce for Checkbox {
         //  - a previously agreed to license that has been updated
         //
         // For the sake of styles we treat the indeterminate state as selected,
-        // but it's icon will be different.
+        // but its icon will be different.
         let selected =
             self.checked == Selection::Selected || self.checked == Selection::Indeterminate;