package/lttng-tools: disable tests

Disabling tests will fix the following build failures on riscv32:

select_poll_epoll.c:408:16: note: each undeclared identifier is reported only once for each function it appears in
select_poll_epoll.c: In function 'ppoll_fds_ulong_max':
select_poll_epoll.c:440:16: error: 'SYS_ppoll' undeclared (first use in this function); did you mean 'SYS_tkill'?
  440 |  ret = syscall(SYS_ppoll, ufds, ULONG_MAX, NULL, NULL);
      |                ^~~~~~~~~
      |                SYS_tkill
select_poll_epoll.c: In function 'pselect_invalid_fd':
select_poll_epoll.c:488:16: error: 'SYS_pselect6' undeclared (first use in this function); did you mean 'SYS_semctl'?
  488 |  ret = syscall(SYS_pselect6, fd + 1, &rfds, NULL, NULL, NULL, NULL);
      |                ^~~~~~~~~~~~
      |                SYS_semctl

Fixes:
 - http://autobuild.buildroot.org/results/dd39188a7191efa512a51f18f4c34d9ee711a6a7



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>