From 2019, GitHub introduced GotHub actions.
So without any third party we are able to automate our deployment process for our private and public git repositories.
We can create workflow (a yml file) to trigger when push to specific branch etc...
This https://engineering.talkdesk.com/test-and-deploy-an-ios-app-with-github-actions-44de9a7dcef6 is a very good tutorial for do this process.
By adding .yml workflow file, we can automate the process of check out source, make build, signing process and submit ipa to test flight.
When you go through the above link, you may face some issues
To see our actions working or not, you will get mail form GitHub if any failure, or you can look at the repositories' 'Actions' (4th) tab. first is 'Code' tab.
Don't forget to set read/write permission for the script file (.sh files)
---Update 1
If you need to update your build number automatically, then use
