fix: logger configuration in service account JWT header

[johannlejeune]

Fix a typo preventing the user from customizing the logger when initializing a new Google::Auth::ServiceAccountJwtHeaderCredentials without a scope

I wasn't able to sign the CLA, got a 400 Bad Request upon form submission, I'll try again later 🤷

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[dazuma]

Thank you for finding this! Let me know if you're still having trouble with the CLA form on a retry.

[johannlejeune]

Thank you for finding this! Let me know if you're still having trouble with the CLA form on a retry.

Tried again, now I'm getting "A server error occurred, please try your request again." 😂

[johannlejeune]

Tried again today, still getting "A server error occurred, please try your request again." ~40s after submitting the form

[johannlejeune]

@dazuma Was finally able to sign it 👍