Interpolation problems in `SourceSerif4[opsz,wght].ttf`

Hello!

This is an automatically-generated report about possible interpolation problems in `SourceSerif4[opsz,wght].ttf`, as found in the Google Fonts catalog.

To download a PDF version of this report with helpful visuals of the problems, click [here](https://github.com/behdad/google-fonts-ofl-interpolatable-results/raw/d56b7371c76cf70a0298bd90323174a7e445a901/reports/SourceSerif4%5Bopsz%2Cwght%5D.ttf.pdf); Or to view it on the GitHub website, click [here](https://github.com/behdad/google-fonts-ofl-interpolatable-results/blob/d56b7371c76cf70a0298bd90323174a7e445a901/reports/SourceSerif4%5Bopsz%2Cwght%5D.ttf.pdf).

The report follows:
```
Glyph uni20A6 was not compatible:
Masters: '', 'opsz=8.0':
Contour 0 structures differ: '', 'opsz=8.0'
```

This report was generated using the `fonttools varLib.interpolatable` tool. We understand that sometimes the tool generates false-positives. Particularly for more complicated font designs. If you did not find this report useful, please accept our apologies and ignore / close it.

To give feedback about this report, please file an issue or open a discussion at [fonttools](https://github.com/fonttools/fonttools).