This action makes sure a milestone is added to a pull request. If there isn't any, the check fails. However it is a shame that there isn't a milestoned event for pull requests so there is not good way to hook this event up.
A best effort config file would look something like this,
name: 'Milestone check'
on:
pull_request:
types: [opened, synchronize, reopened, edited, ready_for_review]
pull_request_review:
types: [submitted]
pull_request_review_comment:
types: [created]
push:
jobs:
check-milestone:
runs-on: ubuntu-latest
steps:
- uses: siimon/milestone-check-action@releases/v2