block code: smaller spacing around center nested in a list.

[u-fischer]

In standard LaTeX center doesn't call \@listii, in the new code it does and this led to a smaller spacing if center is used inside another list:

\DocumentMetadata{}
\documentclass{report}
\begin{document}
\begin{itemize}
\item some text
\begin{center}text \IfDocumentMetadataTF{NEW}{OLD} 
\end{center}
\end{itemize}
\end{document}

gives this difference:

If wanted, this could be probably avoided by surrounding the call with a test for the transparent level:

       \bool_if:NF \l__block_transparent_level_bool
        { \use:c { @list \int_to_roman:n { \g_block_nesting_depth_int } } }