I once wrote an MSBuild script that decompiled a workbook into XML and VBA code. It used a CLI tool I wrote that opened the workbook using VSTO to access the VBA objects.

I never finished it, though. I only spent enough time on it to realize that it was going to be too big of a project to make it worth it.

So now I just rename the workbook to a zip file, extract it, and check that into git. Only drawback is that the VBA macros are in an OLE container. But I stay away from VBA, so it's not that big of a deal for me.