patch 8.2.3967: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more errors to errors.h.
diff --git a/src/scriptfile.c b/src/scriptfile.c
index b932258..c85263e 100644
--- a/src/scriptfile.c
+++ b/src/scriptfile.c
@@ -983,7 +983,7 @@
 
     // ":source" read ex commands
     else if (do_source(fname, FALSE, DOSO_NONE, NULL) == FAIL)
-	semsg(_(e_notopen), fname);
+	semsg(_(e_cant_open_file_str), fname);
 }
 
 /*