This is actually quite easy to implement, I've done it in my fork of this project for huaweicloud, see messense/huaweicloud-github-runner@2354ded

Is there going to be support for matrix jobs in the future? Is there a way to workaround it for now?
For example, if my build is running for java versions:
strategy:
java: [16, 17, 18]

I want to be able to start 3 ec2 slaves and each one of them will have a unique label which will consist of the java version:
${{ needs.start-runner.outputs.label }}_16 ${{ needs.start-runner.outputs.label }}_17 ${{ needs.start-runner.outputs.label }}_18

So I'll be able to run my builds in parallel for each java version