Fix missing keep_in_artist option in ftintitle plugin (introduced in #5356)

[klb2]

Description

Fixes bug introduced in #5356.

The new keep_in_artist option for the ftintitle plugin was introduced in #5356. However, it was not passed to the imported function. (See @chrishoage's comment in #5356).

This is fixed with this PR.

To Do

• [ ] Documentation. (If you've added a new command-line flag, for example, find the appropriate page under docs/ to describe it.)
• [ ] Changelog. (Add an entry to docs/changelog.rst to the bottom of one of the lists near the top of the document.)
• [ ] Tests. (Very much encouraged but not strictly required.)

[github-actions[bot]]

Thank you for the PR! The changelog has not been updated, so here is a friendly reminder to check if you need to add an entry.