Build error on Italic fonts

Hi, my attempts at building this font (`main` branch) always fail for Italics -- it emits lots of warnings of characters being unhinted, and eventually gives me this error:
```
ERROR: Not a valid UFO font at /Italic/Instances/BoldIt/font.ufo
```
And this seems to happen for all the Italic fonts -- the Upright ones were built just fine, I think.
I'm currently using Python 3.11.7.