vtkPythonAnimationCue: add missing Python init call.

vtkPythonAnimationCue was assuming Python was initialized by the time it
got to executing the code. That's not a reasonable assumption. Fixed
that.

Fixes #20413
9 jobs for 20413-python-animation-cue-fixes
Status Name Job ID Coverage
  External
passed cdash-commit

passed ghostflow-branch-check-master

passed ghostflow-branch-check-release

passed cdash-commit

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passed cdash-commit

passed cdash-commit

passed cdash-commit

passed ghostflow-branch-check-master