[css-color-5][editorial] add wpt for color-mix in canvas 2d

Author: svgeesus

css-color-5/Overview.bs

@@ -264,6 +264,9 @@ After normalizing both percentages, the result is produced via the following alg
 	parsing/color-invalid-color-mix-function.html
 	parsing/color-valid-color-mix-function.html
 	parsing/color-mix-out-of-gamut.html
+	/html/canvas/element/fill-and-stroke-styles/2d.fillStyle.colormix.html
+	/html/canvas/element/fill-and-stroke-styles/2d.fillStyle.colormix.currentcolor.html
+	/html/canvas/element/fill-and-stroke-styles/2d.strokeStyle.colormix.html
 </wpt>
 
 The result of mixing is the color at the specified percentage along the progression