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/diff.c b/src/diff.c
index a3bb9c4..59b7891 100644
--- a/src/diff.c
+++ b/src/diff.c
@@ -1319,7 +1319,7 @@
     if (dirbuf[0] != NUL)
     {
 	if (mch_chdir((char *)dirbuf) != 0)
-	    emsg(_(e_prev_dir));
+	    emsg(_(e_cannot_go_back_to_previous_directory));
 	shorten_fnames(TRUE);
     }
 #endif