DOC: Fix typos found by typos and codespell

[yvonnefroehlich]

Description of proposed changes

Fixes of a few typos found by typos and codespell.

Reminders

• Make sure that your code follows our style. Use the other functions/files as a basis.
• Add tests for new features or tests that would have caught the bug that you're fixing.
• Describe changes to function behavior and arguments in a comment below the function declaration.
• If adding new functionality, add a detailed description to the documentation and/or an example.