Missing coverage for Top Level Await

[robpalme]

There's a case where a TLA module and a non-TLA module both dynamically import the same TLA leaf-node module. This fails on JSC but passes on V8 and SM. So it looks like we are missing coverage in test262.

The minimal repro is attached to this bug report as a zip file.

https://bugs.webkit.org/show_bug.cgi?id=242740