This fixes https://github.com/flutter/flutter/issues/139511

* A bug has been fixed with `sync-labels`, meaning this needs to be a boolean now. Setting to `true` to match v4 logic.
* in `labeler.yml`, all labels must be a list of globs, so updated them all to be a list of `any`.
* Update the version to v5

This is a little annoying to test, since the way github actions works means that changes to workflows aren't run until after they are merged. A workaround is I forked these labeler changes to a new branch in my own repo and created a PR to merge to that branch, seen here: https://github.com/drewroengoogle/flutter/actions/runs/7102118110/job/19331743809?pr=2. Note the step `Run actions/labeler@8558fd74291d67161a8a78ce36a881fa63b766a9` which ensures we are running on the latest labeler version in that check.