actions/setup-go resolves 'stable' from the go-versions manifest, which lagged behind the go1.26.6 security release and installed the vulnerable go1.26.5. That both failed govulncheck and broke builds once go.mod required >= 1.26.6 (GOTOOLCHAIN=local). Using go-version-file keeps CI on exactly the toolchain go.mod asks for, which Renovate already keeps current.