patch 8.2.3021: spaces allowed between option name and "!", "?", etc.

Problem:    Spaces allowed between option name and "!", "?", etc.
Solution:   Disallow spaces in Vim9 script, it was not documented.
            (closes #8408)

src/option.c

@@ -1306,9 +1306,10 @@ do_set(
 	    // remember character after option name
 	    afterchar = arg[len];
 
-	    // skip white space, allow ":set ai  ?"
-	    while (VIM_ISWHITE(arg[len]))
-		++len;
+	    if (!in_vim9script())
+		// skip white space, allow ":set ai  ?", ":set hlsearch  !"
+		while (VIM_ISWHITE(arg[len]))
+		    ++len;
 
 	    adding = FALSE;
 	    prepending = FALSE;