Scanner change in #32716 reports errors on jsdoc

```js
/**
 * RegExp to match quoted-pair in RFC 2616
 *
 * quoted-pair = "\" CHAR
 * CHAR        = <any US-ASCII character (octets 0 - 127)>
 * @private
 */
```

**Expected behavior:**
No errors

**Actual behavior:**
Errors on `"\"` (unexpected character) and `@private` ('private' is reserved in strict mode)
