Gateway pinboard.in posts to BlueSky -- as used on https://bsky.app/profile/jmason.ie .
Create a new BlueSky user account (it's good manners to include a line in the bio indicating that it's a bot account).
Copy "envs.sample" to "envs" and fill in the username and password for 'bsky_user' and 'bsky_password'. Fill in the appropriate RSS feed address for your Pinboard account; changing the "u:jm" part to match your username should be all that is needed.
Once this is done, run ". envs; ./gateway.py" as often as necessary; it'll maintain a sqlite database to track which URLs have been previously posted.