patch 8.2.3970: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more errors to errors.h.
diff --git a/src/sign.c b/src/sign.c
index c941544..0656c0f 100644
--- a/src/sign.c
+++ b/src/sign.c
@@ -1630,7 +1630,7 @@
 	    filename = arg;
 	    *buf = buflist_findnr((int)getdigits(&arg));
 	    if (*skipwhite(arg) != NUL)
-		semsg(_(e_trailing_arg), arg);
+		semsg(_(e_trailing_characters_str), arg);
 	    break;
 	}
 	else