GH Actions: automate some issue/PR label management #37
  Add this suggestion to a batch that can be applied as a single commit.
  This suggestion is invalid because no changes were made to the code.
  Suggestions cannot be applied while the pull request is closed.
  Suggestions cannot be applied while viewing a subset of changes.
  Only one suggestion per line can be applied in a batch.
  Add this suggestion to a batch that can be applied as a single commit.
  Applying suggestions on deleted lines is not supported.
  You must change the existing code in this line in order to create a valid suggestion.
  Outdated suggestions cannot be applied.
  This suggestion has been applied or marked resolved.
  Suggestions cannot be applied from pending reviews.
  Suggestions cannot be applied on multi-line comments.
  Suggestions cannot be applied while the pull request is queued to merge.
  Suggestion cannot be applied right now. Please check back later.
  
    
  
    
Description
GH Actions: auto-label new PRs
Similar workflow as the one used in the main PHP_CodeSniffer repo to auto-apply some labels based on the contents of new PRs.
Ref: https://github.com/srvaroa/labeler
GH Actions: automate some label management
This is a quite straight-forward workflow to just remove some labels which should only be on open issues/open PRs and which should be removed once an issue or PR has been closed/merged.
Just attempting to reduce some manual labour.