New client library generation creates a commit without proper author email

[suztomo]

CLA didn't pass for #10264 (comment).

It's not correct to assume google.com account and GitHub user name match in https://github.com/googleapis/google-cloud-java/blob/9785f8cfd43db0a8968f086a1461242da9d16cb5/.github/workflows/generate_new_client.yaml#L114C1-L119C1

      - name: Push to branch and create PR
        run: |
          set -x
          [ -z "`git config user.email`" ] && git config --global user.email "${USERNAME:-script}@google.com"
          [ -z "`git config user.name`" ] && git config --global user.name "${USERNAME:-script}"