ARROW-9059: [Rust] Fix sign in array slice_data_docstring
ARROW-9059: [Rust] Fix sign in array slice_data_docstring

Change the panic behavior in the docstring to reflect the panic behavior in the code

Closes #7369 from robert-wagner/arrow_9059_fix_sign_in_slice_data_docstring

Authored-by: Bobby Wagner <d717d395a7e5851749757a1b2d823fec7f685499@case.edu>
Signed-off-by: Krisztián Szűcs <6bab32dc957a05a87930e779f272342e159326fa@gmail.com>

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