Single file in `contents:` does not render

I don't think this is the most important "bug" to fix; but I figured I would flag. When using a single file in the contents of a section (see example below), that file does not render.

It can be fixed by using a item with - file: about.qmd, but took me about ~30 mins to debug. The reason I bring up the bug at all is that yaml::write_yaml will render a single list item in contents in the form that causes bugs (see example below). This bug impacts the altdoc package (cc @etiennebacher)

Reprex:

1. Run quarto create project website reprex to create simple website.
2. Change _quarto.yml to:

project:
  type: website

website:
  title: "reprex"
  sidebar:
    collapse-level: 1
    style: docked
    contents:
      - text: Home
        file: index.qmd
      - section: Section Header
        contents: about.qmd

format:
  html:
    theme: cosmo
    css: styles.css
    toc: true

Problems with write_yaml

library(yaml)
txt = c(
  "website:",
  "  title: 'reprex'",
  "  sidebar:",
  "    collapse-level: 1",
  "    style: docked",
  "    contents:",
  "      - text: Home",
  "        file: index.qmd",
  "      - section: Section Header",
  "        contents: ",
  "          - about.qmd"
)
yaml = yaml::yaml.load(txt)
file = tempfile()
write_yaml(yaml, file)
cat(readLines(file), sep = "\n")
#> website:
#>   title: reprex
#>   sidebar:
#>     collapse-level: 1
#>     style: docked
#>     contents:
#>     - text: Home
#>       file: index.qmd
#>     - section: Section Header
#>       contents: about.qmd