AWS CodeBuild as Github actions runner – change folder

I have a Github actions workflow that consists of two dependent jobs: Job A does change detection: Which modules in my monorepo changed. Job B is a matrix job, iterating of all changed modules (the working directories are the result of job a) and doing some CI stuff. Now I want to use AWS CodeBuild to run as a self hosted runner for GitHub actions (so I can run everything in my VPC).