Use fixed-size pixel chunks in readonly rendering test

crates/oa-desktop/src/style/tests/readonly.rs

@@ -182,7 +182,9 @@ async fn mounted_readonly_input_keeps_selection_copy_and_readable_paint() {
         let pixels = Headless::screenshot(&mut renderer, Size::new(480, 64), 1.0, BG);
         let style = selectable_input(&theme, text_input::Status::Disabled);
         let selection_pixels: Vec<_> = pixels
-            .chunks_exact(4)
+            .as_chunks::<4>()
+            .0
+            .iter()
             .enumerate()
             .filter(|(_, pixel)| near(pixel, style.selection, 3))
             .map(|(index, _)| (index % 480, index / 480))
@@ -196,7 +198,9 @@ async fn mounted_readonly_input_keeps_selection_copy_and_readable_paint() {
         let top = selection_pixels.iter().map(|p| p.1).min().unwrap();
         let bottom = selection_pixels.iter().map(|p| p.1).max().unwrap();
         let glyph_pixels = pixels
-            .chunks_exact(4)
+            .as_chunks::<4>()
+            .0
+            .iter()
             .enumerate()
             .filter(|(index, pixel)| {
                 let (x, y) = (index % 480, index / 480);