[tests] Xamarin.iOS.Tasks.TargetTests.RebuildExecutable_TouchLibraryDll

msbuild just copies the output assembly from obj to bin. So, the test
needs to `touch` the file in `obj` to trigger a rebuild.

msbuild/tests/Xamarin.iOS.Tasks.Tests/TargetTests/TargetTests.cs

@@ -288,7 +288,7 @@ public void RebuildExecutable_TouchLibraryDll ()
 			RunTarget (MonoTouchProject, TargetName.Build);
 			var timestamps = ExpectedExecutableFiles.ToDictionary (file => file, file => GetLastModified (file));
 
-			Touch (Path.Combine (LibraryProjectBinPath, "MyLibrary.dll"));
+			Touch (Path.Combine (LibraryProjectObjPath, "MyLibrary.dll"));
 			RunTarget (MonoTouchProject, TargetName.Build);
 			var newTimestamps = ExpectedExecutableFiles.ToDictionary (file => file, file => GetLastModified (file));