Highlight n-th \gantttitlelist element in bold

I'm trying to make a pgfgantt chart and highlight the \gantttitlelist elements in regular intervals by making them bold.

To illustrate, here is an example of what I tried:

\documentclass{article}

\usepackage{pgfgantt}

\begin{document}

\begin{ganttchart}{1}{36}
\gantttitle{Months}{36} \\
\gantttitlelist{1,...,36}{1}
\gantttitlelist[title/.style={font=\bfseries}]{12}{1}
\gantttitlelist[title/.style={font=\bfseries}]{24}{1}
\gantttitlelist[title/.style={font=\bfseries}]{36}{1}
\end{ganttchart}

\end{document}


The resulting chart has no bold elements, but I would like that every 12th element, so 12, 24 and 36 are displayed using a bold font.

Any ideas of what I'm missing here?

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