Disabling U+2BC6 and U+2BC8 in folding indicators

Hi, I'm here because [Doom Emacs](https://github.com/doomemacs/doomemacs) migrated to org-modern ([here](https://github.com/doomemacs/doomemacs/commit/b1e6dec47a2d0fa5fd8f7ab55b5f1012d16cb48b)) - heads up that you may have a big influx of users. :) I noticed that you use [folding indicators for headings](https://github.com/minad/org-modern/blob/main/org-modern.el#L69). Third-level headings use U+2BC6 and U+2BC8, which don't render properly with the font I use. I thought this was an issue with my Emacs setup, and spent a while debugging this, before finding the move to `org-modern` and the concept of folding indicators as the source. It seems like these symbols don't exist in many fonts, as they also aren't rendered in GitHub's web interface, or even in [this Unicode directory](https://www.compart.com/en/unicode/U+2BC8)! So my question is: - Would it be possible to use something else? - Failing this, is there a way to override the use of folding indicators in my personal config, and just use headline stars all the time? Thanks a lot!