patch 8.2.2497: no error when using more than one character for a register

Problem:    No error when using more than one character for a register name.
Solution:   In Vim9 script check for a single character string. (closes #7814)
            Fix that VAR_BOOL and VAR_SPECIAL are not considered equal.

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2497,
 /**/
     2496,
 /**/