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/workspace/src/workspace_settings.rs

@@ -12,7 +12,7 @@ pub struct WorkspaceSettings {
     pub confirm_quit: bool,
     pub show_call_status_icon: bool,
     pub autosave: AutosaveSetting,
-    pub restore_on_startup: RestoreOnStartupBehaviour,
+    pub restore_on_startup: RestoreOnStartupBehavior,
     pub drop_target_size: f32,
     pub when_closing_with_no_tabs: CloseWindowWhenNoItems,
     pub use_system_path_prompts: bool,
@@ -43,7 +43,7 @@ impl CloseWindowWhenNoItems {
 
 #[derive(Copy, Clone, Default, Serialize, Deserialize, JsonSchema)]
 #[serde(rename_all = "snake_case")]
-pub enum RestoreOnStartupBehaviour {
+pub enum RestoreOnStartupBehavior {
     /// Always start with an empty editor
     None,
     /// Restore the workspace that was closed last.
@@ -78,7 +78,7 @@ pub struct WorkspaceSettingsContent {
     /// Controls previous session restoration in freshly launched Zed instance.
     /// Values: none, last_workspace, last_session
     /// Default: last_session
-    pub restore_on_startup: Option<RestoreOnStartupBehaviour>,
+    pub restore_on_startup: Option<RestoreOnStartupBehavior>,
     /// The size of the workspace split drop targets on the outer edges.
     /// Given as a fraction that will be multiplied by the smaller dimension of the workspace.
     ///