fix(functions,emulators): loadTriggers() with top level await

[muryoh]

Description

Context: ESM functions with firestore triggers The expected behavior of loadTriggers() is to try and require() the function entrypoint, falling back to dynamic import() when node raises a ERR_REQUIRE_ESM error. But node may also raise an ERR_REQUIRE_ASYNC_MODULE error when the module has top level awaits

This commit simply makes it so ERR_REQUIRE_ASYNC_MODULE also falls back to import()

Scenarios Tested

Tested on our (private) repo

Let me know if tests need to be added/updated :)