Combining characters repeat themselves (`^` + `e` produces `êê`)

It happens in the Web version of the rich text editor.

- Type `^`
- Type `e`

It should produce: `ê`.
It instead produces: `êê`.

[Screen Recording 2024-05-22 at 09.05.44.webm](https://github.com/matrix-org/matrix-rich-text-editor/assets/946104/10bdb926-b2f1-4960-a210-c9925c872137)

