#### Preserve single tildes in Markdown (#19739 by @lazerg)

Since 3.9.0, single-tilde spans like `H~2~O` were rewritten to double tildes, turning subscript syntax into strike-through. Only double tildes are treated that way now, matching GitHub.

<!-- prettier-ignore -->
```markdown
<!-- Input -->
H~2~O

<!-- Prettier stable -->
H~~2~~O

<!-- Prettier main -->
H~2~O
```