patch 8.2.4726: cannot use expand() to get the script name

Problem:    Cannot use expand() to get the script name.
Solution:   Support expand('<script>'). (closes #10121)
diff --git a/src/errors.h b/src/errors.h
index 82c585e..228a1d2 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -3258,3 +3258,5 @@
 #endif
 EXTERN char e_nfa_regexp_missing_value_in_chr[]
 	INIT(= N_("E1273: (NFA regexp) missing value in '\\%%%c'"));
+EXTERN char e_no_script_file_name_to_substitute_for_script[]
+	INIT(= N_("E1274: No script file name to substitute for \"<script>\""));