### Bug description

Using Quarto 1.3.340 on macOS.

Given an `index.qmd` file containing the following content, Quarto attempts to run the embedded R Markdown document.

`````markdown
# Simple Markdown

This is a simple Markdown document containing an embedded R Markdown document.

````markdown
---
title: "making a GET"
---

This shows you how to perform an HTTP connection to some server.

```{r setup, echo = FALSE, include=FALSE}
knitr::opts_chunk$set(echo = TRUE)
```

```{r libraries, echo = FALSE, message = FALSE}
library(httr)
```

```{r fetch, echo = FALSE}
serverURL <- "http://localhost:3939/"

res <- httr::GET(serverURL, httr::write_memory())
if (httr::http_error(res)) {
  err <- sprintf(
    "%s request failed with %s",
    res$request$url,
    httr::http_status(res)$message
  )
  message(capture.output(str(httr::content(res))))
  stop(err)
}
```
````
`````

The resulting error:

```bash
quarto preview index.qmd
#> 
#> 
#> processing file: index.qmd
#>   |..................................................        |  86% [fetch]
#> Quitting from lines 21-33 [fetch] (index.qmd)
#> Error in `curl::curl_fetch_memory()`:
#> ! Failed to connect to localhost port 3939 after 1 ms: Couldn't connect to server
#> Backtrace:
#>  1. httr::GET(serverURL, httr::write_memory())
#>  2. httr:::request_perform(req, hu$handle$handle)
#>  4. httr:::request_fetch.write_memory(req$output, req$url, handle)
#>  5. curl::curl_fetch_memory(url, handle = handle)
#> 
#> Execution halted
```

This document was not meant to be executed. 

```bash
quarto inspect index.qmd | jq .engines
#> [
#>   "knitr"
#> ]
```

### Checklist

- [x] Please include a minimal, fully reproducible example in a single .qmd file? Please provide the whole file rather than the snippet you believe is causing the issue.
- [x] Please [format your issue](https://quarto.org/bug-reports.html#formatting-make-githubs-markdown-work-for-us) so it is easier for us to read the bug report.
- [x] Please document the RStudio IDE version you're running (if applicable), by providing the value displayed in the "About RStudio" main menu dialog?
- [x] Please document the operating system you're running. If on Linux, please provide the specific distribution.
- [x] Please provide the output of `quarto check` so we know which version of quarto and its dependencies you're running.
cscheid
2023-05-18T18:55:39Z
aronatkins
bug ast
Future
open
execution is attempted on document without executable code
https://github.com/quarto-dev/quarto-cli/issues/5603