Use https:// instead of git@ for submodules

[karlseguin]

Allows easily building the project, following the steps in readme, without a github account or having some special git configuration.

If this change is acceptable, I can submit a similar PR for https://github.com/lightpanda-io/zig-js-runtime/blob/main/.gitmodules

[krichprollsch]

Thanks @karlseguin 🙏
We used ssh for submodules when the repos were private. It doesn't makes sense now, you are right.
The similar PR for zig-jsruntime is welcome 👍