Fix some clippy issues found by 1.84.0 (#5603)

crates/egui_extras/src/datepicker/popup.rs

@@ -37,7 +37,7 @@ pub(crate) struct DatePickerPopup<'a> {
     pub highlight_weekends: bool,
 }
 
-impl<'a> DatePickerPopup<'a> {
+impl DatePickerPopup<'_> {
     /// Returns `true` if user pressed `Save` button.
     pub fn draw(&mut self, ui: &mut Ui) -> bool {
         let id = ui.make_persistent_id("date_picker");