patch 8.2.3144: Vim9: no error when using an invalid value for a line number

Problem:    Vim9: no error when using an invalid value for a line number.
Solution:   Give an error if the string value is not recognized.
            (closes #8536)
diff --git a/src/errors.h b/src/errors.h
index 7e823bf..bfbe029 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -498,3 +498,5 @@
 	INIT(= N_("E1207: Expression without an effect: %s"));
 EXTERN char e_complete_used_without_nargs[]
 	INIT(= N_("E1208: -complete used without -nargs"));
+EXTERN char e_invalid_value_for_line_number_str[]
+	INIT(= N_("E1209: Invalid value for a line number: \"%s\""));