ci: make green luacheck

There are different warnings after adding checks and luatest submodules.

Follows-up tarantool/test-run#304

.luacheckrc

@@ -31,6 +31,8 @@ include_files = {
 exclude_files = {
     "build/**/*.lua",
     "test-run/test/test-tarantool/*.test.lua",
+    "test-run/lib/checks/*",
+    "test-run/lib/luatest/*",
     "test/app/*.test.lua",
     "test/box/*.test.lua",
     "test/engine/*.test.lua",