Use US English spelling of "behavior" and "customize" (#15117)

This PR fixes some instances that weren't using US English spellings of
"behavior" and "customize".

Release Notes:

- N/A

crates/project_panel/src/project_panel.rs

@@ -654,7 +654,7 @@ impl ProjectPanel {
 
     pub fn collapse_all_entries(&mut self, _: &CollapseAllEntries, cx: &mut ViewContext<Self>) {
         // By keeping entries for fully collapsed worktrees, we avoid expanding them within update_visible_entries
-        // (which is it's default behaviour when there's no entry for a worktree in expanded_dir_ids).
+        // (which is it's default behavior when there's no entry for a worktree in expanded_dir_ids).
         self.expanded_dir_ids
             .retain(|_, expanded_entries| expanded_entries.is_empty());
         self.update_visible_entries(None, cx);

crates/project_panel/src/project_panel_settings.rs

@@ -60,7 +60,7 @@ pub struct ProjectPanelSettingsContent {
     ///
     /// Default: true
     pub button: Option<bool>,
-    /// Customise default width (in pixels) taken by project panel
+    /// Customize default width (in pixels) taken by project panel
     ///
     /// Default: 240
     pub default_width: Option<f32>,