Pull Request action needs to account for To-do state in order to prepare message

[renehernandez]

When a merged PR is edited, then Basecamp To-dos listed there are being update with an opening comment as follows:

Changes:

• The message should be changed to reflect that PR is already merged, so it will never be completed by this particular PR.
• It should also check if a comment for that PR has already been posted

[renehernandez]

If an open PR contains a link to a completed To-do, then the message added to the basecamp To-do should only mention that is being linked, not that is going to be closed by the PR