[css-speech-1][editorial] Enforce positive <generic-voice> variant using range notation (#14124)

Author: cdoublev

css-speech-1/Overview.bs

@@ -942,7 +942,7 @@ The 'voice-family' property</h3>
 	by specifying match criteria.
 	See the <a href="#voice-selection">voice selection</a> section on this topic.
 
-	<dfn><<generic-voice>></dfn> = <<age>>? <<gender>> <<integer>>?
+	<dfn><<generic-voice>></dfn> = <<age>>? <<gender>> <<integer [1,∞]>>?
 
 	Note: Although the functionality provided by this property is similar to
 	the <a href="https://www.w3.org/TR/speech-synthesis11/#edef_voice"><code>voice</code> element</a>