fixed typo in right_shift description

[Biokastin]

Checklist

• [X] The title and commit message(s) are descriptive.
• [X] Small commits made to fix your PR have been squashed to avoid history pollution.
• [ ] Tests have been added for new features or bug fixes.
• [ ] API of new functions and classes are documented.

Description

Fixes typo in documentation entry for xt::right_shift that incorrectly describes it as if referring to xt::left_shift.