Fix linting

Finally got the eslint job passing here: https://git.drupalcode.org/project/same_page_preview/-/jobs/1647875

That code is part of the Gitlab CI MR here: https://git.drupalcode.org/project/same_page_preview/-/merge_requests/64 I'm hesitant to extract that into a standalone MR over here as it will result in a variety of future merge conflicts. I'd rather just get the remaining jobs passing and get that one through.

I'm going to try to write a blog post about what I did to get this passing - feels like something that will trip others up.

The work is back onto me to figure out remaining phpstan issues.

All done now.

Automatically closed - issue fixed for 2 weeks with no activity.