Returning a disposed HttpResponseMessage takes over 2 minutes

The customer from ICM Incident 232358774 noticed that if a function receives a disposed `HttpResponseMessage` to return, then the function won't return a 502 Bad Gateway immediately, but will instead take over 120 seconds before returning a 502 Bad Gateway response.

This behavior is only observed in Azure and not in local development.

#### Investigative information

Please provide the following:
- Timestamp: 2021-04-27 00:11:59.886
- Function App version: 3.0
- Function App name: vabachuhttpdisposebug
- Function name(s) (as appropriate): HttpTrigger
- Invocation ID: f35c0d00-cea8-496d-b29e-8e54624d28f1
- Region: Central US

(The information above is from an app with the repro that is provided below)

#### Repro

```csharp
public static async Task Run(
[HttpTrigger(AuthorizationLevel.Function, "get", "post", Route = null)] HttpRequest req,
ILogger log)
{
using var request = new HttpRequestMessage(HttpMethod.Get, "https://developers.docusign.com/platform/auth/reference/obtain-access-token/");
using var response = await client.SendAsync(request).ConfigureAwait(false);
// You will see this in the logs in under a second, but function will still be "running"
log.LogInformation("Done");
return response;
}
```

#### Expected behavior
The function should return a 502 Bad Gateway error as soon as the function tries to return the disposed object. In local development, a 500 error is returned within seconds.

#### Actual behavior
The function is Active/Running for over 120 seconds before returning a 502 error. This behavior is observed in Azure.

#### Known workarounds
None

Start with the provided C# HttpTrigger reproduction and compare its local behavior with execution in Azure. Done means returning the disposed HttpResponseMessage produces the expected 502 without the observed 120-second delay; no specific files or tests are named in the issue.

Written by the indexing model from the issue text.