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.
diff --git a/src/version.c b/src/version.c
index 3c9edfd..55dd8d1 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2497,
+/**/
     2496,
 /**/
     2495,