Adding heading to markdown field scrolls to the top in Safari

**Describe the bug**
After adding header to markdown editor browser scrolls to the top of the field. Only in Safari.

**To Reproduce**
1. Open Safari browser;
2. Add markdown field to admin with default settings;
3. Add a lot of text to the markdown field;
4. Insert heading in the end of markdown content;
5. Browser scrolls to top.

**Expected behavior**
Browser scroll stays in place.

**Screenshots**
[Link to screencast (Google Drive)](https://drive.google.com/file/d/1iLcTdyo6NarK1ro83ni6dW2mrFhQvSyH/view?usp=sharing)

**Applicable Versions:**
- Netlify CMS 2.10.102
- Safari 14.03