Nextra crashes if props are used within headings

[nikischin]

Nextra crashes if props are used within headings:

## Someheading containing {props.someProp}

Will produce an error like this:

Cannot read properties of undefined (reading 'props.someProp')
...
export function useTOC(props) {
  13 |   return [{
> 14 |     value: <>{"Someheading containing "}{props.someProp}</>,

Still persists in v4

Taken from @nikischin in #3749 (comment)