lib/compression: Include missing stat header file

lib/compression: Include missing stat header file

<sys/stat.h> was missing from compression library tests which resulted
in the following compile time error:

../../lib/compression/tests/test_lzx_huffman.c: In function
                                                   ‘datablob_from_file’:
../../lib/compression/tests/test_lzx_huffman.c:383:21: error:
                                         storage size of ‘s’ isn’t known
  383 |         struct stat s;
      |                     ^
../../lib/compression/tests/test_lzx_huffman.c:389:15: warning:
    implicit declaration of function ‘fstat’ [-Wimplicit-function-declaration]
  389 |         ret = fstat(fileno(fh), &s);
      |               ^~~~~

Signed-off-by: Anoop C S <anoopcs@samba.org>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Volker Lendecke <vl@samba.org>
Autobuild-User(master): Volker Lendecke <vl@samba.org>
Autobuild-Date(master): Tue Dec  6 11:39:16 UTC 2022 on sn-devel-184