Improve valid-milestone-change workflow

[richard-cox]

Summary

• remove org level permission (this was the reason for the 'no jobs run' notification on forks due to it failing)
• org level permission not allowed with defaut gh token, so replace with our vault one
• remove the 'edit' milestone change trigger. we might still need this but lets start smaller
• remove vs code lint warnings via defining envs up front
• use echo delimiter and toJSON to avoid injection vulnerabilities

Technical notes summary

• follows on from
  • Add workflow to notify slack of milestone changes made by those external to team #15328
  • Updates to valid milestone change workflow #16059
• supersedes
  • Remove already disabled GitHub Action workflow #17761

Areas or cases that should be tested

• the workflow is currently disabled, and also only outputs to a slack target that just DMs me
• once merged i'll enable the the workflow again and test

Checklist

• The PR is linked to an issue and the linked issue has a Milestone, or no issue is needed
• The PR has a Milestone
• The PR template has been filled out
• The PR has been self reviewed
• The PR has a reviewer assigned
• The PR has automated tests or clear instructions for manual tests and the linked issue has appropriate QA labels, or tests are not needed
• The PR has reviewed with UX and tested in light and dark mode, or there are no UX changes
• The PR has been reviewed in terms of Accessibility
• The PR has considered, and if applicable tested with, the three Global Roles Admin, Standard User and User Base

[marcelofukumoto]

I didnt execute the WORKFLOW, just checking line by line and trying to check code structure.

[marcelofukumoto]

Question
just comparing with the previous flow. The OLD_MILESTONE sets the value to

echo "OLD_MILESTONE=${{ github.event.milestone.title }}"

This one sets to $ISSUE_MILESTONE which. is...

        ISSUE_MILESTONE: ${{ github.event.issue.milestone.title }}

It is different. Not sure about the logic, So mostly pointing out this difference.

[richard-cox]

had pondered about that too. went with the assumption it was a typo when originally created. don't think i've seen a full run of this yet, so in all worlds will require some test / fix cycles