check the stderr writes errcheck now sees

cmd/catalog-impact/main.go

@@ -149,18 +149,18 @@ func run(ctx context.Context, out, errOut io.Writer, opts *options) error {
 // stays clean.
 func warn(w io.Writer, r *impact.Result) {
 	for _, file := range r.UnmappedFiles {
-		fmt.Fprintf(w, "warning: %s matches no mapping rule; every host is included\n", file)
+		_, _ = fmt.Fprintf(w, "warning: %s matches no mapping rule; every host is included\n", file)
 	}
 	for _, line := range impact.UnresolvedLines(r.UnresolvedRefs) {
-		fmt.Fprintf(w, "warning: %s did not resolve to a class name; the host list may be incomplete\n", line)
+		_, _ = fmt.Fprintf(w, "warning: %s did not resolve to a class name; the host list may be incomplete\n", line)
 	}
 	for _, line := range r.NodeWarnings {
-		fmt.Fprintf(w, "warning: %s; the estate table may be missing hosts\n", line)
+		_, _ = fmt.Fprintf(w, "warning: %s; the estate table may be missing hosts\n", line)
 	}
 	for _, class := range r.OrphanClasses {
-		fmt.Fprintf(w, "warning: class %s is declared by nothing and listed in no hiera_include; it reaches no hosts\n", class)
+		_, _ = fmt.Fprintf(w, "warning: class %s is declared by nothing and listed in no hiera_include; it reaches no hosts\n", class)
 	}
 	if r.Truncated {
-		fmt.Fprintf(w, "warning: %d hosts affected, output capped at %d by --limit\n", r.Summary.Hosts, len(r.Hosts))
+		_, _ = fmt.Fprintf(w, "warning: %d hosts affected, output capped at %d by --limit\n", r.Summary.Hosts, len(r.Hosts))
 	}
 }