Don't update nox in 'tasks/synth.py'. (#6232)
Don't update nox in 'tasks/synth.py'. (#6232)

Closes #6224.
GoogleCloudPlatform/gcloud-python,GoogleCloudPlatform/gcloud-python,dhermes/gcloud-python,googleapis/google-cloud-python,tswast/google-cloud-python,googleapis/google-cloud-python,jonparrott/gcloud-python,dhermes/google-cloud-python,dhermes/google-cloud-python,tseaver/google-cloud-python,jonparrott/gcloud-python,jonparrott/google-cloud-python,jonparrott/google-cloud-python,tswast/google-cloud-python,tseaver/google-cloud-python,tseaver/google-cloud-python,dhermes/google-cloud-python,tswast/google-cloud-python,dhermes/gcloud-python