patch 8.2.4012: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move the last error messages to errors.h.
diff --git a/src/sign.c b/src/sign.c
index 42592a4..1be1d13 100644
--- a/src/sign.c
+++ b/src/sign.c
@@ -1224,7 +1224,7 @@
     }
     else
     {
-	semsg(_("E885: Not possible to change sign %s"), sign_name);
+	semsg(_(e_not_possible_to_change_sign_str), sign_name);
 	return FAIL;
     }
 
@@ -1307,7 +1307,7 @@
 
 	if (buf->b_fname == NULL)
 	{
-	    emsg(_("E934: Cannot jump to a buffer that does not have a name"));
+	    emsg(_(e_cannot_jump_to_buffer_that_does_not_have_name));
 	    return -1;
 	}
 	cmd = alloc(STRLEN(buf->b_fname) + 25);