The Build/Lint/Race jobs checked out viperblock and predastore at a hardcoded
ref: dev and overlaid them with a go workspace, so the go.mod pins were ignored
and a spinifex change depending on an unmerged sibling change could never
compile in CI. Resolve each sibling to a branch of the same name when it exists
on that repo, else dev, mirroring the e2e path in
scripts/tofu-cluster/build-install-artifacts.sh so unit CI and e2e CI agree.