Clippy: as_chunks in the signature image test (follow-up to #335) (#360)

Signed-off-by: Chiranjeevi U <244287281+chiranjeevi-max@users.noreply.github.com>

crates/engine/src/signature_image.rs

@@ -152,7 +152,7 @@ mod tests {
         let image = SignatureImage::from_bytes(&jpeg.into_inner()).unwrap();
         assert_eq!(image.size(), [60, 20]);
         assert!(image.bytes().starts_with(b"\x89PNG\r\n\x1a\n"));
-        assert!(image.rgba().chunks_exact(4).all(|p| p[3] == 255));
+        assert!(image.rgba().as_chunks::<4>().0.iter().all(|p| p[3] == 255));
     }
 
     #[test]