internal/pkg: DCE benchmark unwrap only

This eliminates noise at lower depths.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pkg/pkg_test.go

@@ -1622,9 +1622,10 @@ func BenchmarkEarlyDCE(b *testing.B) {
 		b.Fatalf("Cure: error = %v", err)
 	}
 	c.Close()
+	dce := err.(*pkg.DependencyCureError)
 
 	for b.Loop() {
-		err.Error()
+		dce.Unwrap()
 	}
 }