Bug#945475: the autopkgtests fail due to a deprecation warning on stderr

[Sebastien Bacher]

Package: liblouisxml
Version: 2.4.0-9

Since the stderr restriction has been added back in -9 the tests fail in
Ubuntu
https://objectstorage.prodstack4-5.canonical.com/v1/AUTH_77e2ada1e7a84929a74ba3b87153c0ac/autopkgtest-focal/focal/amd64/libl/liblouisxml/20191104_095709_0acde@/log.gz

'command1             FAIL stderr:
/usr/share/liblouis/tables/en-chardefs.cti:181: warning: \Xhhhh (with a
capital 'X') is deprecated.'

Cheers,