Describe the bug
When minimized a simple egui application will use up to 17% CPU on my CPU while using 0% when not minimized

To Reproduce
Steps to reproduce the behavior:

1. Take a very simple egui application:

use eframe::egui;

fn main() -> Result<(), eframe::Error> {
    let options = eframe::NativeOptions {
        viewport: egui::ViewportBuilder::default().with_inner_size([320.0, 240.0]),
        ..Default::default()
    };

    eframe::run_simple_native("My egui App", options, move |ctx, _frame| {
        egui::CentralPanel::default().show(ctx, |ui| {
            ui.heading("My egui Application");
        });
    })
}

2. Run it
3. Observe CPU usage while open, if the mouse cursor is not in the window it will drop to 0
4. Minimize window
5. CPU Usage will go up a lot

Expected behavior
CPU Usage should stay low or at least close to the same CPU Usage when not minized

Screenshots
When idle and not minimized:

After being minimized:

Desktop:

• OS: Windows 10 21H2 (19044.3086)
• Version: latest master (56bf8b7)

Additional context
This does not happen with 0.25