Normative: FlagText allows s (#1123)

spec.html

@@ -12175,7 +12175,7 @@ <h1>Static Semantics: Early Errors</h1>
             It is a Syntax Error if BodyText of |RegularExpressionLiteral| cannot be recognized using the goal symbol |Pattern| of the ECMAScript RegExp grammar specified in <emu-xref href="#sec-patterns"></emu-xref>.
           </li>
           <li>
-            It is a Syntax Error if FlagText of |RegularExpressionLiteral| contains any code points other than `"g"`, `"i"`, `"m"`, `"u"`, or `"y"`, or if it contains the same code point more than once.
+            It is a Syntax Error if FlagText of |RegularExpressionLiteral| contains any code points other than `"g"`, `"i"`, `"m"`, `"s"`, `"u"`, or `"y"`, or if it contains the same code point more than once.
           </li>
         </ul>
       </emu-clause>