.github/actions/dynamic/action.yaml

name: Dynamic
description: Dynamically resolves another GitHub action
inputs:
  action:
    description: Action reference
    required: true
  with:
    description: Action inputs as multi-line YAML string
    required: false
    default: ""
outputs:
  outputs:
    description: JSON object of outputs from the action
    value: ${{ steps.run.outputs.outputs }}
runs:
  using: composite
  steps:
    - name: Instantiate
      shell: bash
      run: |
        # Dynamically invoke ${{ inputs.action }}
        with='${{ inputs.with }}'
        [[ -z "$with" ]] || with="$(echo '    with:'; sed -e 's/^/      /' <<<"$with")"
        mkdir -p ./.tmp/dynamic-action-instance
        cat <<END >./.tmp/dynamic-action-instance/action.yaml
        runs:
          using: composite
          steps:
          - id: run
            uses: ${{ inputs.action }}
        $with
        outputs:
          outputs:
            value: $(echo '$'){{ toJSON(steps.run.outputs) }}
        END
    - name: Run
      id: run
      uses: ./.tmp/dynamic-action-instance