Fix intermediate color in color-mix(red yellow 65%) example.

The main bug was reported both in a comment in the spec and in
w3ctag/design-reviews#526 (comment)

This also fixes dropping of a "9" digit in the red's chroma midway
through the calculations.

Note that the correct intermediate is well out of sRGB.  I just chose to
use it anyway and add a note about such cases.

css-color-5/Overview.bs

@@ -187,6 +187,10 @@ If no keyword is specified, it is as if ''shorter'' were specified.
 	keeps the intermediate colors
 	as saturated as the endpoint colors.
 
+	Note: Some of the intermediate colors (including the one shown)
+	are outside of the sRGB gamut
+	and may not display correctly across implementations.
+
 	<pre class="lang-css">color-mix(red yellow 65%);</pre>
 
 	<figure>
@@ -205,17 +209,10 @@ If no keyword is specified, it is as if ''shorter'' were specified.
 		* sRGB  <span class="swatch" style="--color: red"></span> red (#F00) is lch(54.2917% 106.8390 40.8526)
 		* sRGB <span class="swatch" style="--color: yellow"></span>  yellow (#FF0) is lch(97.6071% 94.7077 99.5746)
 		* mixed lightness is 54.2917 * 0.65 + 97.6071 * 0.35 = 69.4521
-		* mixed chroma is 106.83 * 0.65 + 94.7077 * 0.35 = 102.5872
+		* mixed chroma is 106.8390 * 0.65 + 94.7077 * 0.35 = 102.5930
 		* mixed hue is 40.8526 * 0.65 + 99.5746 * 0.35 = 61.4053
-		* mixed result is lch(69.4521% 102.5872 61.4053)
-		* which is a red-orange: <span class="swatch" style="--color: rgb(75.3600% 65.6304% 16.9796%)"></span>  rgb(75.3600% 65.6304% 16.9796%)
-		<!-- no it isn't!
-		orange_lch=[69.4521, 102.5872, 61.4053]
-		Array(3) [ 69.4521, 102.5872, 61.4053 ]
-
-		orange_srgb=LCH_to_sRGB(orange_lch)
-		Array(3) [ 1.0437490814854606, 0.5037070457407858, -0.3096435504814653 ]
-		-->
+		* mixed result is lch(69.4521% 102.5930 61.4053)
+		* which is a red-orange: <span class="swatch" style="--color: rgb(104.3765% 50.3695% -30.9644%)"></span>  rgb(104.3765% 50.3695% -30.9644%)
 </div>
 
 Instead of mixing all channels equally, color-adjusters can be used