Disable SelectionLabels test if Python is disabled

This fixes a test failure for the SelectionLabels which fails
if Python is not enabled. Now the test should only be run if
ParaView is built with Python support.

Change-Id: Iee16e0e4d1642e8990b12302a923f37d4ea47a40
Merge topic 'fix-selection-test' into next

db520d5 Disable SelectionLabels test if Python is disabled