Pgfgantt remove labels of month

Question

My project has a 6 years duration and I want to realise a Gantt chart still readable in the width of the A4 page, in portrait format.

I want to remove the labels (the numbers) in the month line of the Gantt chart, and just keep empty cells of the table in my pgfgantt chart.

\documentclass{article}
\RequirePackage{pgfgantt}
\begin{document}
\begin{ganttchart}[time slot format=isodate-yearmonth, 
    vgrid={dotted,draw=none,draw=none}, %hgrid=true, 
    x unit=0.22cm,          % NOTE: width for a single month
    y unit chart = 0.6cm, bar height=0.6,
    y unit title = 0.5cm, title height=1,
    include title in canvas=false,
    time slot unit=month
    ]{2024-09}{2030-09}  %project duration
% temporal marks
\gantttitlecalendar[title/.style={fill=black!30,draw=black}]{year} \\
\gantttitlecalendar[title/.style={fill=black!20,draw=black}]{month} \\

\end{ganttchart}
\end{document}