Detected a unquoted template variable as an attribute. If unquoted, a malicious actor could inject custom JavaScript handlers. To fix this, add quotes around the template expression, like this: "{{ expr }}".
<link {{ if not (isset . "rel") }}rel="stylesheet" {{ end }}{{ range $key, $value := . }} {{ if eq $key "href" }}{{ (printf "%s=\"%s\"" $key ($value | absURL)) | safeHTMLAttr }}{{ else }}{{ (printf "%s=\"%s\"" $key (string $value)) | safeHTMLAttr }}{{ end }}{{ end }}>