Posting data to the DAG is pretty straight forward but to create an oracle that would post any GitHub update to the dag would probably be a quite costly approach since each transaction on the dag has a small fee.

The solution to this often is to create a subscription based oracle that will listen on the external platform's API only for updates it knows users would need.

For the use case suggested, the bot that the repository owner use to create the task bounty should also notify the oracle that it want to subscribe to that specific event. This enablea the oracle to not have to scan entire github but to focus on only one repository and probably one specific event (like the merge event) and then post that to the dag.

Another approach could be to have the bot trigger the post event. This will require one of the parties of the smart contract to ask the bot to get the oracle to post a specific piece of data. The flights delay oracle works like that. When the passenger or insurror wants to retrieve their money, they connect to the bot and ask it to post data on a given departure.

The flight insurance oracle can be found on GitHub and there's a template oracle here