Clients should allow scopes to be set via client_options.

The scopes provided should override the scopes of the OAuth access token.

from google.cloud import texttospeech

client = texttospeech.textToSpeechClient(
    client_options={"scopes": ["..", "..."]}
)

Internal link: go/extensible-client-options-exit

Many credentials types prohibit modifying the scopes on the original credential, so we will use with_scopes.