enable test16_opaque_handle (#156)

This reverts commit f67ab83.

Author: Vipul-Cariappa

test/test_fragile.py

@@ -399,7 +399,6 @@ def test15_const_in_name(self):
         assert cppyy.gbl.myvar3
         assert cppyy.gbl.myvar4
 
-    @mark.xfail(run=False, reason="Crashes sometimes; might have been caused by https://github.com/compiler-research/CPyCppyy/pull/109")
     def test16_opaque_handle(self):
         """Support use of opaque handles"""