Fix for the `mask_treatment` parameter documentation in the BoxcarExtract docstring. #706

Job	Run time
tests / Load tox environments	8s
tests / Codestyle	19s
tests / Python 3.10 on Linux with oldest supported dependencies	1m 12s
tests / Python 3.10 on Windows with minimal dependencies	1m 44s
tests / Python 3.10 on OSX with minimal dependencies	51s
tests / Python 3.11 on Linux with all dependencies, remote data, and coverage	1m 22s
tests / (Allowed Failure) Python 3.12 on Linux with dev dependencies	2m 17s
	7m 53s

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