AlembicSceneTest::testCancel : Loosen timing tolerance to account for debug CI build

Author: danieldresser-ie

contrib/IECoreAlembic/test/IECoreAlembic/AlembicSceneTest.py

@@ -1934,7 +1934,7 @@ def backgroundRun():
 		canceller.cancel()
 		thread.join()
 
-		self.assertLess( time.time() - startTime, 0.06 )
+		self.assertLess( time.time() - startTime, 0.1 if IECore.isDebug() else 0.06 )
 		self.assertTrue( cancelled[0] )
 
 	def testIndexedCurveUVs( self ) :