Check Lua source code with luacheck

```
Checking test-run/lib/tarantool-python/test-run/lib/tarantool-python/tests/suites/box.lua 1 warning

    test-run/lib/tarantool-python/test-run/lib/tarantool-python/tests/suites/box.lua:2:1: (W121) setting read-only global variable os

```

Tarantool issue: https://github.com/tarantool/tarantool/issues/4681