raylib keyboard: fix double period

[sshane]

@deanlee interested in this? In the special chars view there's two periods that use the same widget so clicking is inconsistent. We can replace with a different char if it's the easiest fix

[deanlee]

this issue was fixed in the #36361 by replacing duplicate periods with alternative characters.

However, a more robust approach would be to use position-based keys (e.g., f"{layout}{row_idx}{col_idx}") to uniquely identify each key position. This would eliminate all duplicate key issues, and prevent button objects from being overwritten when the same character appears in multiple layouts.

But since the current solution works, we can focus our efforts elsewhere for now.