Based on Yihue's StackOverflow answer from about 5 years ago, you can do the following: Fence the whole code section with four backticks, and add `r''` to the beginning of each code chunk. Here's what the document looks like. (Incidentally, I had to fence this whole example with five backticks in order to display it properly.)
---
title: "Hello, Tutorial!"
output: learnr::tutorial
runtime: shiny_prerendered
---
```{r setup, include=FALSE}
library(learnr)
```
````
---
title: "Hello, Tutorial!"
output: learnr::tutorial
runtime: shiny_prerendered
---
`r ''````{r setup, include=FALSE}
library(learnr)
```
This code computes the answer to one plus one, change it so it computes two plus two:
`r ''````{r addition, exercise=TRUE}
1 + 1
```
````
Here's what the output looks like: