Improve the caching transport tests (#4360)

The caching transport tests can fail when running the device tests if the simulator looses network connectivity. This PR changes the test to use a `FakeReliableNetworkStatusListener ` implementation of `INetworkStatusListener` that ignores the real network status and just pretends that everything is OK, so that test reliability isn't impacted by network connectivity.

Extracted from #4294

#skip-changelog

Author: jamescrosswell

test/Sentry.Testing/FakeReliableNetworkStatusListener.cs

@@ -0,0 +1,20 @@
+namespace Sentry.Testing;
+
+/// <summary>
+/// To be used when we don't want the real network status to affect the reliability of our tests
+/// </summary>
+public class FakeReliableNetworkStatusListener : INetworkStatusListener
+{
+    public static readonly FakeReliableNetworkStatusListener Instance = new();
+
+    private FakeReliableNetworkStatusListener()
+    {
+    }
+
+    public bool Online => true;
+
+    public Task WaitForNetworkOnlineAsync(CancellationToken cancellationToken)
+    {
+        return Task.CompletedTask;
+    }
+}