Fix for the `mask_treatment` parameter documentation in the BoxcarExtract docstring. #707

Job	Run time
tests / Load tox environments	7s
tests / Codestyle	13s
tests / Python 3.10 on Linux with oldest supported dependencies	1m 1s
tests / Python 3.10 on Windows with minimal dependencies	1m 29s
tests / Python 3.10 on OSX with minimal dependencies	51s
tests / Python 3.11 on Linux with all dependencies, remote data, and coverage	1m 10s
tests / (Allowed Failure) Python 3.12 on Linux with dev dependencies	1m 33s
	6m 24s

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