Deadlock in Microsoft.AspNetCore.Mvc.Testing on .NET 7

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Describe the bug

The following combination causes a deadlock when trying to read `HttpContext.Request.Body`:

* NET 7 (`7.0.100`)
* `Microsoft.AspNetCore.Mvc.Testing` (`7.0.0`)
* Using the `Microsoft.AspNetCore.Hosting.HttpRequestIn.Start` `DiagnosticListener` event.
* Using **synchronous** IO to read the request body (e.g. `ReadToEnd()`).

The code snippet below is from the [linked reproducer sample](https://github.com/z1c0/Mvc.TestingHang).
The call to `ReadToEnd()` hangs forever.

```cs
internal class KeyValueObserver : IObserver>
{
public void OnNext(KeyValuePair kvp)
{
if (kvp.Key == "Microsoft.AspNetCore.Hosting.HttpRequestIn.Start")
{
var context = kvp.Value as HttpContext;

var bodyControlFeature = context.Features.Get();
bodyControlFeature.AllowSynchronousIO = true;

var stream = new StreamReader(context.Request.Body);
var body = stream.ReadToEnd(); // Hangs forever!
body.ToString();
}
}
}
```

Running the same code with previous versions of .NET (Core) works without a problem.

### Expected Behavior

The call should not hang as with previous versions.

### Steps To Reproduce

Reproducer project: https://github.com/z1c0/Mvc.TestingHang
Run the unit test method `BasicTests.TestPost`.
* NET 7.0: The test hangs forever
* NET 6.0: The test terminates and the request body can be read correctly.

### Exceptions (if any)

_No response_

### .NET Version

7.0.100

### Anything else?

I could reproduce the problem on Windows, Linux, and macOS.
The same code worked fine with previous versions (.NET Core 3.1, .NET 5.0, .NET 6.0 on all platforms).