You don't need to create a new SSH public key for your robot user when using Codeship. Once you've completed the steps for CI Integration, set up Codeship as follows:
Step 1: Copy the public key from your Codeship project's General Settings page, and add it as a new key for your robot user.
Step 2: Add a Custom Script deployment in Codeship with the following commands:
git fetch --depth=1000000 git push email@example.com:$ENVIRONMENT_HANDLE/$APP_HANDLE.git $CI_COMMIT_ID:master
📘 In the above example,
firstname.lastname@example.org:$ENVIRONMENT_HANDLE/$APP_HANDLE.gitrepresents your app's Git Remote.
Also, see My deploy failed with a git error referencing objects, trees, revisions or commits to understand why you need