False positive: it is valid to escape $ in javascript template string syntax

**Description of the false positive**

js/useless-regexp-character-escape triggers for code like:

```javascript
const str = `hello \${name}`;
```

This is invalid, since without the backslash escape, that's a string interpolation of the `name` variable:

```javascript
const str = `hello ${name}`;
```

This triggered in the lit-html codebase on this line: https://github.com/lit/lit/blob/5eea178e0df1199cd29e9d46bc888d52882f18dd/packages/lit-html/src/lit-html.ts#L1418

Link to the code scanning issue: https://github.com/lit/lit/security/code-scanning/15