md and markdown are different output formats - this is confusing

Bug description

quarto render index.qmd --to md and quarto render index.qmd --to markdown produce different output.

Steps to reproduce

Consider the minimal working example where index.qmd is

---
title: MWE
---

## Section
This is a simple placeholder for the manuscript's main document.

Run quarto render index.qmd --to md --output md_output and quarto render index.qmd --to markdown --output markdown_output.

Run diff markdown_output md_output.

Expected behavior

markdown_output and md_output will be the same.

Actual behavior

1,4c1
< ---
< title: MWE
< toc-title: Table of contents
< ---
---
> # MWE
8c5
< This is a simple placeholder for the manuscript's main document.
---
> This is a simple placeholder for the manuscript’s main document.

Your environment

• Ubuntu

Quarto check output

[✓] Checking versions of quarto binary dependencies...
      Pandoc version 3.1.2: OK
      Dart Sass version 1.55.0: OK
      Deno version 1.33.2: OK
[✓] Checking versions of quarto dependencies......OK
[✓] Checking Quarto installation......OK
      Version: 1.4.126
      Path: /opt/quarto/bin

[✓] Checking basic markdown render....OK

ERROR: YAMLError: unexpected end of the stream within a double quoted scalar at line 3, column 1:
    
    ^

Stack trace:
    
    ^
    at generateError (file:///opt/quarto/bin/quarto.js:10487:12)
    at throwError (file:///opt/quarto/bin/quarto.js:10490:11)
    at readDoubleQuotedScalar (file:///opt/quarto/bin/quarto.js:10836:12)
    at composeNode (file:///opt/quarto/bin/quarto.js:11309:125)
    at readBlockMapping (file:///opt/quarto/bin/quarto.js:11124:17)
    at composeNode (file:///opt/quarto/bin/quarto.js:11306:84)
    at readDocument (file:///opt/quarto/bin/quarto.js:11420:5)
    at loadDocuments (file:///opt/quarto/bin/quarto.js:11455:9)
    at load (file:///opt/quarto/bin/quarto.js:11460:23)
    at parse3 (file:///opt/quarto/bin/quarto.js:11470:12)