vello_tests: use as_chunks in WebGL texture target tests

vello_tests/tests/webgl_texture_target.rs

diff --git a/vello_tests/tests/webgl_texture_target.rs b/vello_tests/tests/webgl_texture_target.rs
index 1c25f78..d236fce 100644
--- a/vello_tests/tests/webgl_texture_target.rs
+++ b/vello_tests/tests/webgl_texture_target.rs
@@ -44,7 +44,11 @@
 fn assert_all(pixels: &[u8], color: AlphaColor<Srgb>) {
     let expected = color.to_rgba8().to_u8_array();
     assert!(
-        pixels.chunks_exact(4).all(|pixel| pixel == expected),
+        pixels
+            .as_chunks::<4>()
+            .0
+            .iter()
+            .all(|pixel| *pixel == expected),
         "expected every pixel to be {expected:?}, got {pixels:?}"
     );
 }