Wrong substitution for Cyrillic io + combining mark

[frankrolf]

As mentioned by @codepointless here: #72 (comment)

io + combining mark results in wrong base glyph.
The problem is a bug in the ccmp feature – these are the lines responsible:

https://github.com/adobe-fonts/source-serif/blob/main/Roman/familyGSUB.fea#L474
https://github.com/adobe-fonts/source-serif/blob/main/Italic/familyGSUB.fea#L457

[frankrolf]

Leaving this open until new fonts exist.

[frankrolf]

Fixed in 4.005: https://github.com/adobe-fonts/source-serif/releases/tag/4.005R