Don't automatically update test262 submodule

[richarddd]

When quickjs-ng now is used a dependency of rquickjs, cargo automatically pulls in all submodules when checking out sources. This causes errors on windows hosts where the filepath becomes to long:

path too long: 'C:/Users/runneradmin/.cargo/git/checkouts/rquickjs-c5d9b5f474075f2d/9e0229a/sys/quickjs/test262/test/built-ins/Object/seal/object-seal-configurable-attribute-of-own-data-property-of-o-is-set-from-true-to-false-and-other-attributes-of-the-property-are-unaltered.js'; class=Filesystem (30)

[saghul]

I guess our CI doesn't download it automagically now. Can you fix that please? LGTM otherwise.