MDEV-14425 fixup: mariabackup.huge_lsn,strict_crc32 rdiff

Some old versions of "patch" (such as patch 2.5.9 on Microsoft Windows)
require that a file name header be present.
To ensure that the diff will be applied, let us add the header.

mysql-test/suite/mariabackup/huge_lsn,strict_crc32.rdiff

+--- suite/mariabackup/huge_lsn.result
++++ suite/mariabackup/huge_lsn.reject
 @@ -1,8 +1,8 @@
  #
  # MDEV-13416 mariabackup fails with EFAULT "Bad Address"