\PushDefaultHookLabel{.}

## Brief outline of the bug

At the top level both `\SetDefaultHookLabel{top-level}`, `\SetDefaultHookLabel{.}` an `\PushDefaultHookLabel{top-level}` raise but not `\PushDefaultHookLabel{.}`
```
\documentclass{minimal}
\begin{document}
\PushDefaultHookLabel{.}
\PopDefaultHookLabel
\end{document}
```
`lthooks` from 2022/11/30
