Fix flakiness in RequestsCanBeAbortedMidRead (#4881)

Addresses dotnet/aspnetcore-internal#1521

Author: halter73

src/Servers/Kestrel/test/FunctionalTests/RequestTests.cs

@@ -1206,7 +1206,12 @@ await connection.Send("POST / HTTP/1.1",
                 }
             }
 
-            await Assert.ThrowsAsync<TaskCanceledException>(async () => await readTcs.Task);
+            var thrownEx = await Assert.ThrowsAnyAsync<Exception>(async () => await readTcs.Task);
+
+            // https://github.com/aspnet/AspNetCore-Internal/issues/1521
+            // In more recent versions of Kestrel, we expect this to always be a TaskCanceledException,
+            // but without the changes in https://github.com/aspnet/KestrelHttpServer/pull/2844, this is flaky.
+            Assert.True(thrownEx is TaskCanceledException || thrownEx is IOException, $"{thrownEx} is neither a TaskCanceledException nor IOException.");
 
             // The cancellation token for only the last request should be triggered.
             var abortedRequestId = await registrationTcs.Task;