[ci] Update path for generated *.include.* files

[jonpryor]

Context: a7b5768
Context: a0b7aad

Ever since commit a0b7aad, the Prepare .NET Release > Push Internal job has been failing:

Step Xamarin.Android.Prepare.Step_CopyExtraResultFilesForCI failed: Could not find a part of the path 'D:\a\_work\1\s\src\monodroid\jni'.
System.InvalidOperationException: Step Xamarin.Android.Prepare.Step_CopyExtraResultFilesForCI failed: Could not find a part of the path 'D:\a\_work\1\s\src\monodroid\jni'.
 ---> System.IO.DirectoryNotFoundException: Could not find a part of the path 'D:\a\_work\1\s\src\monodroid\jni'.
   at System.IO.Enumeration.FileSystemEnumerator`1.CreateDirectoryHandle(String path, Boolean ignoreNotFound)
   at System.IO.Enumeration.FileSystemEnumerator`1.Init()
   at System.IO.Enumeration.FileSystemEnumerable`1..ctor(String directory, FindTransform transform, EnumerationOptions options, Boolean isNormalized)
   at System.IO.Enumeration.FileSystemEnumerableFactory.UserFiles(String directory, String expression, EnumerationOptions options)
   at System.IO.Directory.InternalEnumeratePaths(String path, String searchPattern, SearchTarget searchTarget, EnumerationOptions options)
   at System.IO.Directory.GetFiles(String path, String searchPattern, EnumerationOptions enumerationOptions)
   at Xamarin.Android.Prepare.Step_CopyExtraResultFilesForCI.CopyExtraBuildFiles(String destinationRoot, Context context) in D:\a\_work\1\s\build-tools\xaprepare\xaprepare\Steps\Step_CopyExtraResultFilesForCI.cs:line 72
   at Xamarin.Android.Prepare.Step_CopyExtraResultFilesForCI.<>c__DisplayClass1_0.<Execute>b__0() in D:\a\_work\1\s\build-tools\xaprepare\xaprepare\Steps\Step_CopyExtraResultFilesForCI.cs:line 24
   at System.Threading.ExecutionContext.RunFromThreadPoolDispatchLoop(Thread threadPoolThread, ExecutionContext executionContext, ContextCallback callback, Object state)
--- End of stack trace from previous location ---
   at System.Threading.ExecutionContext.RunFromThreadPoolDispatchLoop(Thread threadPoolThread, ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.Tasks.Task.ExecuteWithThreadLocal(Task& currentTaskSlot, Thread threadPoolThread)
--- End of stack trace from previous location ---
   at Xamarin.Android.Prepare.Step_CopyExtraResultFilesForCI.Execute(Context context) in D:\a\_work\1\s\build-tools\xaprepare\xaprepare\Steps\Step_CopyExtraResultFilesForCI.cs:line 22
   at Xamarin.Android.Prepare.Step.Run(Context context) in D:\a\_work\1\s\build-tools\xaprepare\xaprepare\Application\Step.cs:line 42
   at Xamarin.Android.Prepare.Scenario.Run(Context context, Log log) in D:\a\_work\1\s\build-tools\xaprepare\xaprepare\Application\Scenario.cs:line 37
   --- End of inner exception stack trace ---
   at Xamarin.Android.Prepare.Scenario.Run(Context context, Log log) in D:\a\_work\1\s\build-tools\xaprepare\xaprepare\Application\Scenario.cs:line 48
   at Xamarin.Android.Prepare.Context.Execute() in D:\a\_work\1\s\build-tools\xaprepare\xaprepare\Application\Context.cs:line 511
   at Xamarin.Android.Prepare.App.Run(String[] args) in D:\a\_work\1\s\build-tools\xaprepare\xaprepare\Main.cs:line 162

The InvalidOperationException is thrown because commit a7b5768 reorganized things; src/monodroid/jni no longer exists, and thus attempting to read that directory will fail.

Update Step_CopyExtraResultFilesForCI.CopyExtraBuildFiles() to instead look for src/native/monodroid/*.include.* files. This should fix the InvalidOperationException.

[pjcollins]

LGTM -- the other issues affecting this job should hopefully be addressed by commit f834b55 and https://portal.microsofticm.com/imp/v3/outages/details/506472816/overview when resolved