[Bug]: cannot parse indented content

### What happened?

zx fails with `SyntaxError: Unexpected identifier 'assumes'` when given the following markdown file: https://github.com/wighawag/template-ethereum-contracts/blob/593bb65e0c3ebffaff0d1c4b938c48003a5cdfdc/README.md?plain=1

### How it should work?

it should parse it and execute what is in the code blocks

### How to reproduce the bug?

create a file README.md with the content above

and execute

```
zx README.md
```

### Version

8.8.5

### What's OS kind?

Linux

### What JS runtime is used?

Node.js

### Runtime Version

24.11.1

### Error stack / relevant log output

```shell
SyntaxError: Unexpected identifier 'assumes'
```

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct