tests: cover baecd1cf2685 ("segtree: Fix segfault when restoring a huge interval...

tests: cover baecd1cf2685 ("segtree: Fix segfault when restoring a huge interval set")

Test inspired by [1] with both the set and stack size reduced by the
same power of 2, to preserve the (pre-baecd1cf2685) segfault on one
hand, and make the test successfully complete (post-baecd1cf2685) in a
few seconds even on weaker hardware on the other.

(The reason I stopped at 128kB stack size is that with 64kB I was
getting segfaults even with baecd1cf2685 applied.)

[1] https://bugzilla.redhat.com/show_bug.cgi?id=1908127

Signed-off-by: Štěpán Němec <snemec@redhat.com>
Helped-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Phil Sutter <phil@nwl.cc>