Set tests as hermetic

I'm not able to reproduce the failure locally. It appears the test is failing though because it's picking up the global interpreter constraint which is causing a failure? We'll see if this works.

tests/python/pants_test/backend/python/tasks/test_pytest_run_integration.py

@@ -20,6 +20,10 @@
 class PytestRunIntegrationTest(PantsRunIntegrationTest):
   testproject = 'testprojects/src/python/interpreter_selection'
 
+  @classmethod
+  def hermetic(cls):
+    return True
+
   def test_pytest_run_timeout_succeeds(self):
     pants_run = self.run_pants(['clean-all',
                                 'test.pytest',

tests/python/pants_test/backend/python/tasks/test_python_run_integration.py

@@ -21,6 +21,10 @@
 class PythonRunIntegrationTest(PantsRunIntegrationTest):
   testproject = 'testprojects/src/python/interpreter_selection'
 
+  @classmethod
+  def hermetic(cls):
+    return True
+
   @skip_unless_python3
   @ensure_daemon
   def test_run_3(self):