Pull Request Labeler is not working

[alamb]

Describe the bug
The automatic labeler job (in Dev PR / "Process") https://github.com/apache/arrow-rs/blob/master/.github/workflows/dev_pr.yml#L23-L39 is supposed to label Pull Requests based on what files they change, but it does not appear to be working

To Reproduce
Make a PR

Expected behavior
PRs should automatically be labeled with arrow, parquet, etc labels depending on what files are changed;

Additional context
The labeler came from the original in arrow: https://github.com/apache/arrow/blob/master/.github/workflows/dev_pr.yml#L65-L74

Which seems to be working

[Dandandan]

Checking the difference yields:

on:
  # TODO: Enable this when eps1lon/actions-label-merge-conflict is available.
  # push:
  #   branches:
  #     - master
  pull_request_target:
    types:
      - opened
      - edited
      - synchronize

This version:

on:
  pull_request: