Typo: "kiby" instead of "kivy" in global variable in _text_pango.pyx

[Xovaryu]

This is just a typo fix for the line global kiby_fontfamily_cache, the kiby instead of kivy being the typo. I don't use Pango myself and it seems a little odd that this typo is in the code when it looks like it might break something? Someone may want to have a look into this.

Maintainer merge checklist

• [x] Title is descriptive/clear for inclusion in release notes.
• [x] Applied a Component: xxx label.
• [ ] Applied the api-deprecation or api-break label.
• [ ] Applied the release-highlight label to be highlighted in release notes.
• [x] Added to the milestone version it was merged into.
• [ ] Unittests are included in PR.
• [ ] Properly documented, including versionadded, versionchanged as needed.

[welcome[bot]]

Thanks for opening your first pull request here! 💖 Please check out our contributing guidelines.

[welcome[bot]]

Congrats on merging your first pull request! 🎉🎉🎉