patch 8.2.1506: Vim9: no error when using a number other than 0 or 1 as bool

Problem:    Vim9: no error when using a number other than 0 or 1 as bool.
Solution:   Check the number is 0 or 1.
diff --git a/src/errors.h b/src/errors.h
index a49aa73..ffcbdef 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -73,7 +73,8 @@
 	INIT(= N_("E1021: const requires a value"));
 EXTERN char e_type_or_initialization_required[]
 	INIT(= N_("E1022: type or initialization required"));
-// E1023 unused
+EXTERN char e_using_number_as_bool_nr[]
+	INIT(= N_("E1023: Using a Number as a Bool: %d"));
 EXTERN char e_using_number_as_string[]
 	INIT(= N_("E1024: Using a Number as a String"));
 EXTERN char e_using_rcurly_outside_if_block_scope[]