[browser][MT] Runtime Aborts after executing Program::Main()

[glutio]

Description

The multithreading browser runtime crashes in await runMain() after executing Program::Main().

Reproduction Steps

.csproj

<Project Sdk="Microsoft.NET.Sdk.WebAssembly">
  <PropertyGroup>
    <TargetFramework>net9.0</TargetFramework>
    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
    <WasmEnableThreads>true</WasmEnableThreads>
  </PropertyGroup>
</Project>

.js

import { dotnet } from './_framework/dotnet.js'
const { runMain } = await dotnet.create();
await runMain();

.cs

using System;
Console.WriteLine("Hello, Browser!");

Expected behavior

Prints message and does not crash

Actual behavior

Prints message and crashes

worker.onerror		@	dotnet.native.9.0.0-…8.5.kpnkj0mqsi.js:8
error (async)		
(anonymous)		@	dotnet.native.9.0.0-…8.5.kpnkj0mqsi.js:8
loadWasmModuleToWorker	@	dotnet.native.9.0.0-…8.5.kpnkj0mqsi.js:8
e.loadWasmModuleToWorker@	ui-thread.ts:243
Bn			@	ui-thread.ts:359
(anonymous)		@	ui-thread.ts:169
(anonymous)		@	startup.ts:247

dotnet.native.wasm:1  Uncaught (in promise) RuntimeError: unreachable
    at __trap (dotnet.native.wasm)
    at ___trap (dotnet.native.9.0.0-preview.4.24202.8.804phjyibc.js:7325:45)
    at abort (dotnet.native.9.0.0-preview.4.24202.8.804phjyibc.js:727:3)
    at _abort (dotnet.native.9.0.0-preview.4.24202.8.804phjyibc.js:5423:2)
    at ves_icall_System_Environment_FailFast (dotnet.native.wasm)
    at ves_icall_System_Environment_FailFast_raw (dotnet.native.wasm)
    at do_icall (dotnet.native.wasm)
    at do_icall_wrapper (dotnet.native.wasm)
    at mono_interp_exec_method (dotnet.native.wasm)
    at interp_runtime_invoke (dotnet.native.wasm)

Regression?

Works in .net8

Known Workarounds

No response

Configuration

version 9.0.x-preview.x

Other information

No response

[maraf]

cc @pavelsavara

[pavelsavara]

The real error is Marshalling null return Task to JS is not supported in MT because the void Main() doesn't create any task.