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/testing.c b/src/testing.c
index 782d35c..f401863 100644
--- a/src/testing.c
+++ b/src/testing.c
@@ -433,7 +433,7 @@
     fd1 = mch_fopen((char *)fname1, READBIN);
     if (fd1 == NULL)
     {
-	vim_snprintf((char *)IObuff, IOSIZE, (char *)e_notread, fname1);
+	vim_snprintf((char *)IObuff, IOSIZE, (char *)e_cant_read_file_str, fname1);
     }
     else
     {
@@ -441,7 +441,7 @@
 	if (fd2 == NULL)
 	{
 	    fclose(fd1);
-	    vim_snprintf((char *)IObuff, IOSIZE, (char *)e_notread, fname2);
+	    vim_snprintf((char *)IObuff, IOSIZE, (char *)e_cant_read_file_str, fname2);
 	}
 	else
 	{