[css-color-hdr] Correct 2100-pq black luminance to ≤ 0.005 cd/m², fix w3c#10459

Author: svgeesus

css-color-hdr/Overview.bs

@@ -380,7 +380,7 @@ Predefined color spaces for HDR: {#predefined-HDR}
 		<tr><th>Transfer function</th><td colspan="2">Perceptual Quantizer</td></tr>
 		<tr><th>White luminance</th><td colspan="2">203 cd/m²</td></tr>
 		<tr><th>Peak white luminance</th><td colspan="2">10,000 cd/m²</td></tr>
-		<tr><th>Black luminance</th><td colspan="2">0.001 cd/m²</td></tr>
+		<tr><th>Black luminance</th><td colspan="2">≤ 0.005 cd/m²</td></tr>
 		<tr><th>Image state</th><td colspan="2">display-referred</td></tr>
 		<tr>
 			<th>Percentages</th>