Fix docs warning

[bdice]

Description

Closes https://github.com/rapidsai/rmm/issues/1705.

Checklist

• [x] I am familiar with the Contributing Guidelines.
• [x] New or existing tests cover these changes.
• [x] The documentation is up to date with these changes.

[bdice]

Yay! This fixed the docs builds. I will merge this.

[bdice]

/merge