[css-images-4][editorial] Add missing wpt

Author: svgeesus

css-images-4/Overview.bs

@@ -2996,6 +2996,7 @@ Changes Since Level 3</h3>
 	animation/image-no-interpolation.html
 	animation/object-position-interpolation.html
 	animation/object-view-box-interpolation.html
+	animation/image-slice-interpolation-math-functions-tentative.html
 	image-fit-001.xht
 	image-fit-006.xht
 	image-orientation/image-orientation-background-image.html