Fix install of installed-tests, now in /usr/libexec/

This is now the default since debhelper compat 12:
The build system autoconf no longer explicitly set the --libexecdir
variable and thus relies on the build system default - which should
be /usr/libexec (per FHS 3.0, adopted in Debian Policy 4.1.5).

See: https://manpages.debian.org/bookworm/debhelper/debhelper-compat-upgrade-checklist.7.en.html#v12



Signed-off-by: Dylan Aïssi <dylan.aissi@collabora.com>

debian/libtraprain-0-tests.install

-usr/lib/*/installed-tests/traprain-0
+usr/libexec/installed-tests/traprain-0
 usr/share/installed-tests/traprain-0
 etc/apparmor.d/usr.lib.installed-tests.traprain.test-mock-service