Wrong preview url used when `_quarto.yml` is present

Bug description

When _quarto.yml is present (even if empty) a wrong preview url is used even though the correct one is displayed after running quarto preview test.qmd. (I use the VSCode extension)

Possibly related: https://github.com/quarto-dev/quarto-cli/issues/6409

Steps to reproduce

Create an empty _quarto.yml and a test.qmd like

---
title: "Test"
---

# abc

and run quarto preview test.qmd.

When choosing either preview option (Editor / Browser) it tries to open the URL http://127.0.0.1:<port>/ while the preview command actually shows http://localhost:<port>/test.html as the correct URL.

Expected behavior

Use correct URL to preview

Actual behavior

Wrong URL is used to preview

Your environment

• IDE: VSCode Version: 1.91.0
• devcontainer on Macos running debian 12 (bookworm)

Quarto check output

# quarto check
Quarto 1.5.54
[✓] Checking versions of quarto binary dependencies...
      Pandoc version 3.2.0: OK
      Dart Sass version 1.70.0: OK
      Deno version 1.41.0: OK
      Typst version 0.11.0: OK
[✓] Checking versions of quarto dependencies......OK
[✓] Checking Quarto installation......OK
      Version: 1.5.54
      Path: /opt/quarto/bin

[✓] Checking tools....................OK
      TinyTeX: v2024.07.03
      Chromium: (not installed)

[✓] Checking LaTeX....................OK
      Using: TinyTex
      Path: /root/.TinyTeX/bin/x86_64-linux
      Version: 2024

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

[✓] Checking Python 3 installation....OK
      Version: 3.12.4 (Conda)
      Path: /opt/conda/bin/python
      Jupyter: 5.7.2
      Kernels: python3

[✓] Checking Jupyter engine render....OK

[✓] Checking R installation...........(None)

      Unable to locate an installed version of R.
      Install R from https://cloud.r-project.org/

Start at the preview URL handling used by quarto preview test.qmd and the VSCode Editor/Browser preview options, using the empty _quarto.yml reproduction. Compare the URL shown by the command with the URL opened by the extension; done means the preview opens http://localhost:<port>/test.html rather than the server root.