Improve stability of remove_task_decorator function

[romsharon98]

closes: #34154
cc: @SamWheating

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[jscheffl]

Thanks for the fix, even did not know about this bug. Thanks also for the TODO; I assume there should be better options to parse the source code other than cutting by keywords.

[SamWheating]

Thanks for reviving this old PR, I totally forgot about it but I'm glad to see that its back up for review 🙌

FWIW I still think that this is an imperfect solution (and anything which relies on manipulating code as a plain string probably will be), but it should at least fix the reported error without introducing new failures.

See additional notes in #34509.

[romsharon98]

Thanks for the fix, even did not know about this bug. Thanks also for the TODO; I assume there should be better options to parse the source code other than cutting by keywords.

I only fixed a small test, the credits goes to @SamWheating