New PR template requires Add labels and milestones, but it is impossible because non-maintainer author do not have labelling permission.
Try to follow below PR template instruction as non-maintainer.
- [ ] Add labels and milestones (and optionally projects) to the PR so it can be classified; _Bugfixes should be including in bug-fix release milestones (m.f.X) and features should be included in (m.X.b) releases._
non-maintainer author do not have permission, so can do nothing (no label setup icon, like below image).

Have labelling permission, so PR author can label the PR.
master latest (5e09fd31e9850902fc0a79e92aaba7b80dae1944)
This template description is introduced in #4523
cc @Borda
Hey @tarepan,
Don't worry, we added this line to make sure Pytorch Ligthning Core Team add labels on every PRs.
Best regards,
Thomas Chaton.
@tchaton this is in the section for reviewers so do not worry... :]
but maybe we should write it there that the before submit is for author and PR review is for reviewers only