[tests] Ignore NSUrlSessionHandlerTest.DisposeAndRecreateBackgroundSessionHandler if the background session is in use.

Hopefully fixes this test failure:

    [FAIL] DisposeAndRecreateBackgroundSessionHandler :   Second request exception
      Expected: null
      But was:  <System.Net.Http.HttpRequestException: Could not communicate with background transfer service
      ---> Foundation.NSErrorException: Error Domain=NSURLErrorDomain Code=-996 "Could not communicate with background transfer service" UserInfo={_NSURLErrorRelatedURLSessionTaskErrorKey=(
           "BackgroundDataTask <FE008EA4-3168-4E2F-B066-9565EEC47E67>.<1>"
          ), NSLocalizedDescription=Could not communicate with background transfer service, _NSURLErrorFailingURLSessionTaskErrorKey=BackgroundDataTask <FE008EA4-3168-4E2F-B066-9565EEC47E67>.<1>}
      --- End of inner exception stack trace ---
      at System.Net.Http.NSUrlSessionHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) in /Users/builder/azdo/_work/4/s/macios/src/Foundation/NSUrlSessionHandler.cs:line 595
      at System.Net.Http.HttpClient.GetByteArrayAsyncCore(HttpRequestMessage request, CancellationToken cancellationToken)
      at MonoTests.System.Net.Http.NSUrlSessionHandlerTest.<>c.<<DisposeAndRecreateBackgroundSessionHandler>b__0_1>d.MoveNext() in /Users/builder/azdo/_work/1/s/macios/tests/monotouch-test/System.Net.Http/NSUrlSessionHandlerTest.cs:line 47
      --- End of stack trace from previous location ---
      at TestRuntime.TryRunAsync(TimeSpan timeout, Task startTask, Task completionTask, UIImage imageToShow, Exception& exception) in /Users/builder/azdo/_work/1/s/macios/tests/common/TestRuntime.RunAsync.cs:line 119>
      at MonoTests.System.Net.Http.NSUrlSessionHandlerTest.DisposeAndRecreateBackgroundSessionHandler() in /Users/builder/azdo/_work/1/s/macios/tests/monotouch-test/System.Net.Http/NSUrlSessionHandlerTest.cs:line 60

Author: rolfbjarne

tests/monotouch-test/System.Net.Http/NSUrlSessionHandlerTest.cs

@@ -37,6 +37,7 @@ public void DisposeAndRecreateBackgroundSessionHandler ()
 				Assert.Inconclusive ("First request failed or timed out - cannot verify the bug.");
 			}
 
+			IgnoreIfExceptionDueToBackgroundServiceInUseByAnotherProcess (ex);
 			TestRuntime.IgnoreInCIIfBadNetwork (ex);
 			Assert.IsNull (ex, "First request exception");
 
@@ -56,8 +57,26 @@ public void DisposeAndRecreateBackgroundSessionHandler ()
 				Assert.Fail ("Second request timedout - this indicates the bug is present.");
 			}
 
+			IgnoreIfExceptionDueToBackgroundServiceInUseByAnotherProcess (ex);
 			TestRuntime.IgnoreInCIIfBadNetwork (ex);
 			Assert.IsNull (ex, "Second request exception");
 		}
+
+		void IgnoreIfExceptionDueToBackgroundServiceInUseByAnotherProcess (Exception? e)
+		{
+			if (e is null)
+				return;
+
+			if (e is not HttpRequestException hre)
+				return;
+
+			if (hre.InnerException is not NSErrorException nee)
+				return;
+
+			if (nee.Code != (nint) NSUrlError.BackgroundSessionInUseByAnotherProcess)
+				return;
+
+			Assert.Ignore ("The background service is in use by another process.");
+		}
 	}
 }