Defining custom macros is not possible with Katex

Bug description

Enabling katex for doesn't expand macros

Steps to reproduce

---
format:
  html:
    html-math-method: katex
    include-in-header:
       text: |
        $$\newcommand{\E}{\mathbb{E}}$$
---

$\E$

Expected behavior

---
format:
  html:
    # html-math-method: katex
    include-in-header:
       text: |
        $$\newcommand{\E}{\mathbb{E}}$$
---

$\E$

Actual behavior

Your environment

• Quarto 1.4.489
• macOS Sonoma

Quarto check output

Quarto 1.4.489
[✓] Checking versions of quarto binary dependencies...
Pandoc version 3.1.8: OK
Dart Sass version 1.55.0: OK
Deno version 1.33.4: OK
[✓] Checking versions of quarto dependencies......OK
[✓] Checking Quarto installation......OK
Version: 1.4.489
Path: /Applications/quarto/bin

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

[✓] Checking LaTeX....................OK
Using: Installation From Path
Path: /Library/TeX/texbin
Version: 2022

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

[✓] Checking Python 3 installation....OK
Version: 3.11.4
Path: /opt/homebrew/opt/python@3.11/bin/python3.11
Jupyter: 5.5.0
Kernels: python3

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

[✓] Checking R installation...........OK
Version: 4.2.0
Path: /Library/Frameworks/R.framework/Resources
LibPaths:
- /Library/Frameworks/R.framework/Versions/4.2-arm64/Resources/library
knitr: (None)
rmarkdown: (None)

  The rmarkdown package is not available in this R installation.
  Install with install.packages("rmarkdown")