luacheck: fix warnings in test/box-py

Closes #5456

Reviewed-by: Vladislav Shpilevoy <v.shpilevoy@tarantool.org>
Reviewed-by: Igor Munkin <imun@tarantool.org>

Co-authored-by: Vladislav Shpilevoy <v.shpilevoy@tarantool.org>
Co-authored-by: Igor Munkin <imun@tarantool.org>

.luacheckrc

@@ -39,7 +39,6 @@ exclude_files = {
     "test/box/lua/require_mod.lua",
     -- Unused source file, to be dropped (gh-5169).
     "test/box/lua/test_init.lua",
-    "test/box-py/**/*.lua",
     "test/box-tap/**/*.lua",
     "test/engine/**/*.lua",
     "test/engine_long/**/*.lua",

test/box-py/box.lua

 #!/usr/bin/env tarantool
-os = require('os')
+local os = require('os')
 
 box.cfg{
     listen              = os.getenv("LISTEN"),