Our DockerHub password is in ESC, and a bunch of the other variables
were copy-pasted defaults. We need to keep GCP because that isn't in
ESC yet.
Refs https://github.com/pulumi/ci-mgmt/issues/1583.
This PR was automatically generated by the
update-workflows-single-bridged-provider workflow in the pulumi/ci-mgmt
repo, from commit e43a0e1c1f44e3e431240deb0ac363cf172ae9a9.