Fix syntax bug of cssVariable example in fonts.mdx

[chrissy-dev]

Description (required)

Missing , - breaks when copying and pasting.

[netlify]

✅ Deploy Preview for astro-docs-2 ready!

Built without sensitive environment variables

Name	Link
🔨 Latest commit	176b714
🔍 Latest deploy log	https://app.netlify.com/projects/astro-docs-2/deploys/69492990b2ddc50008ddd7a8
😎 Deploy Preview	https://deploy-preview-12967--astro-docs-2.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify project configuration.

[astrobot-houston]

Lunaria Status Overview

🌕 This pull request will trigger status changes.

Learn more

By default, every PR changing files present in the Lunaria configuration's files property will be considered and trigger status changes accordingly.

You can change this by adding one of the keywords present in the ignoreKeywords property in your Lunaria configuration file in the PR's title (ignoring all files) or by including a tracker directive in the merged commit's description.

Tracked Files

File	Note
en/reference/experimental-flags/fonts.mdx	Source changed, localizations will be marked as outdated.

Warnings reference

Icon	Description
🔄️	The source for this localization has been updated since the creation of this pull request, make sure all changes in the source have been applied.

[astrobot-houston]

Hello! Thank you for opening your first PR to Astro’s Docs! 🎉

Here’s what will happen next:

1. Our GitHub bots will run to check your changes.
   If they spot any broken links you will see some error messages on this PR.
   Don’t hesitate to ask any questions if you’re not sure what these mean!

2. In a few minutes, you’ll be able to see a preview of your changes on Netlify 🥳.

3. One or more of our maintainers will take a look and may ask you to make changes.
   We try to be responsive, but don’t worry if this takes a few days.

[ArmandPhilippot]

Thank you for spotting this, and welcome to Team Docs! 🥳