[css-values-3] fix minor typo (w3c#7481)

"This unquoted syntax ~is~ cannot accept a <url-modifier> argument ..."

Author: 12Me21

css-values-3/Overview.bs

@@ -558,7 +558,7 @@ Resource Locators: the <<url>> type</h3>
 		</pre>
 	</div>
 
-	Note: This unquoted syntax is cannot accept a <<url-modifier>> argument
+	Note: This unquoted syntax cannot accept a <<url-modifier>> argument
 	and has extra escaping requirements:
 	parentheses, <a href="https://www.w3.org/TR/css-syntax/#whitespace">whitespace</a> characters,
 	single quotes (&#39;) and double quotes (") appearing in a URL