[tests] Ignore failing test Issue18751Test on android (#33620)

### Description of Change

Test Issue18751Test is flacky and failing on Android 

tracking issue here #33507

Author: rmarinho

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue18751.cs

@@ -1,4 +1,4 @@
-#if TEST_FAILS_ON_IOS && TEST_FAILS_ON_CATALYST && TEST_FAILS_ON_WINDOWS //related issues: https://github.com/dotnet/maui/issues/33507, https://github.com/dotnet/maui/issues/15994
+#if TEST_FAILS_ON_IOS && TEST_FAILS_ON_CATALYST && TEST_FAILS_ON_WINDOWS && TEST_FAILS_ON_ANDROID //related issues: https://github.com/dotnet/maui/issues/33507, https://github.com/dotnet/maui/issues/15994
 using NUnit.Framework;
 using UITest.Appium;
 using UITest.Core;