patch 8.2.3975: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more error messages to errors.h.
diff --git a/src/sign.c b/src/sign.c
index 0656c0f..290d414 100644
--- a/src/sign.c
+++ b/src/sign.c
@@ -1019,7 +1019,7 @@
     // Currently sign text must be one or two display cells
     if (s != endp || cells < 1 || cells > 2)
     {
-	semsg(_("E239: Invalid sign text: %s"), text);
+	semsg(_(e_invalid_sign_text_str), text);
 	return FAIL;
     }