Disabling System.Diagnostics.Process.MainModule test against Issue#1896

EnumProcessModules which is used internally for getting the list of process modules
and main module. This API is a best effort API which may not work in certain scenarios.
I am still debating whether we should have test for this in our CI.
For now, I am disabling this against an Issue#1896 while I gather more data
on whether it makes sense to remove the test completely.

Author: Pallavi Taneja

src/System.Diagnostics.Process/tests/System.Diagnostics.Process.Tests/ProcessTest.cs

@@ -225,6 +225,7 @@ public void Process_MachineName()
         }
 
         [Fact]
+        [ActiveIssue(1896, PlatformID.Windows)]
         public void Process_MainModule()
         {
             // Get MainModule property from a Process object