test: temporary disable on_shutdown.test.lua test

The test is flaky and often fails in parallel testing. We want to enable
parallel testing within scope of #4156 (enabling GitLab CI).

It should be enabled back in the scope of #4134.

Needed for #4156.

test/box/suite.ini

@@ -2,7 +2,7 @@
 core = tarantool
 description = Database tests
 script = box.lua
-disabled = rtree_errinj.test.lua tuple_bench.test.lua
+disabled = rtree_errinj.test.lua tuple_bench.test.lua on_shutdown.test.lua
 release_disabled = errinj.test.lua errinj_index.test.lua rtree_errinj.test.lua upsert_errinj.test.lua iproto_stress.test.lua
 lua_libs = lua/fifo.lua lua/utils.lua lua/bitset.lua lua/index_random_test.lua lua/push.lua lua/identifier.lua
 use_unix_sockets = True