patch 8.2.4044: Vim9: no error when importing the same script twice

Problem:    Vim9: no error when importing the same script twice.
Solution:   Give an error, unless it is a reload.
diff --git a/src/errors.h b/src/errors.h
index 9facb82..8e7ffee 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -2891,3 +2891,5 @@
 	INIT(= N_("E1260: Cannot unlet an imported item: %s"));
 EXTERN char e_cannot_import_dot_vim_without_using_as[]
 	INIT(= N_("E1261: Cannot import .vim without using \"as\""));
+EXTERN char e_cannot_import_same_script_twice_str[]
+	INIT(= N_("E1262: Cannot import the same script twice: %s"));