[3.9] Type unions squeeze into a single line

I've enjoyed using Prettier for a long time, but I recently tried upgrading to prettier 3.9, but a lot of our code was reformatted to squeeze type untions into a single line for some reason? I think it's this one https://github.com/prettier/prettier/pull/18827, but it results in much worse formatted code, both for git diffs and readability.

v3.8

export type WorkerJob =
  | UpdateDataJob
  | UpdateEventsJob
  | UpdateOtherJob
  | UpdateSearchJob
  | UpdatePopularJob;

v3.9

export type WorkerJob =
  UpdateDataJob  | UpdateEventsJob  | UpdateOtherJob  | UpdateSearchJob  | UpdatePopularJob;

This 3.9 version is worse, since any changes in the type will now result in the whole line being git-diffed, while the old one had a proper diff & history tracking foreach union member.

Reproduce the formatting difference with the TypeScript union example in this issue using Prettier 3.8 and 3.9, then review the behavior change in pull request #18827. Trace the formatter path responsible for type unions and add or update a regression test showing that each union member remains on its own line; done means the 3.9 output preserves the readable multiline form.