test: disable override checks

NO_DOC=Test update
NO_CHANGELOG=Test update

test/app-luatest/checks_test.lua

+-- luatest installs external checks module.
+-- After https://github.com/tarantool/checks/pull/54,
+-- external checks will override built-in one, yet
+-- we want to test built-in one here.
 local rock_utils = require('third_party.checks.test.rock_utils')
+rock_utils.remove_override('checks')
 rock_utils.assert_builtin('checks')
 
 require('third_party.checks.test.test')