muster release v5.23.5

go install github.com/giantswarm/muster/v5@latest builds the release it resolves to. Go refuses go install <package>@<version> for a module whose go.mod carries a replace directive, and go.mod carried one since 2026-08-28: goldmark pinned to a fixed version for the nancy scan, because golang.org/x/tools required a version OSS Index flagged (#1106). Nothing in the build reaches x/tools or goldmark anymore (go mod why -m github.com/yuin/goldmark: the main module does not need it; neither is among the packages go list -deps ./... hands to nancy), so the pin changed nothing but the go install verdict and is gone. The module graph is unchanged.