output file name conflict when two formats targets same extension (like html and revealjs)

Bug description

When defining both html and revealjs formats in the config (_quarto.yml), if format is not defined in individual qmd files, it gives this error:

ERROR: NotFound: No such file or directory (os error 2), rename '/home/user/Desktop/test/report.html' -> '/home/user/Desktop/test/_site/report.html'

To reproduce, create three files:

_quarto.yml

project:
  type: website

website:
  title: "Test"

format:
  html:
    theme: "flatly"
  revealjs:
    theme: "beige"

presentation.qmd

---
title: "Presentation"
format: revealjs
---

## Slide 1

This is a presentation

## Slide 2

More contents here

report.qmd

---
title: "Report"
---

## Heading 1

This is a report

Then run quarto render. Adding format: html to report.qmd fixes this issue.

It took me a while to troubleshoot as the error message was not helpful.

🢒  quarto --version
1.2.1

🢒  lsb_release -a
No LSB modules are available.
Distributor ID:	Zorin
Description:	Zorin OS 16.2
Release:	16
Codename:	focal

Checklist

• 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.
• Please format your issue so it is easier for us to read the bug report.
• Please document the RStudio IDE version you're running (if applicable), by providing the value displayed in the "About RStudio" main menu dialog?
• Please document the operating system you're running. If on Linux, please provide the specific distribution.

Reproduce the conflict using _quarto.yml, presentation.qmd, and report.qmd, then run quarto render with both html and revealjs formats configured. Confirm that the report output collides and produces the rename error; done means rendering succeeds without requiring format: html in report.qmd and both outputs are written correctly.