### Bug description

Quarto version: 1.1.189
System: WSL (Windows 10) with Ubuntu terminal

The added subscription is not loaded in post pages as it does in the main blog page. 

I'm adding `margin-header: subscribe.html ` under `website` section in `_quarto.yml`.  

In the posts, only the filename "subscribe.html" appears instead of loading the file! You can see this in the screenshot below. You can check the HTML  code from the Developer inspect tool.
![blog_post](https://user-images.githubusercontent.com/30320825/194929036-76915865-f462-4ecd-a978-162000556d22.png)

FYI, the main blog page works fine as can be seen below. 
![blog_page](https://user-images.githubusercontent.com/30320825/194928994-cb8456de-9a71-44ee-9c22-ab3abc1b6a79.png)


### 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](https://quarto.org/bug-reports.html#formatting-make-githubs-markdown-work-for-us) 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.
2022-10-10T18:19:37Z
e-alizadeh
bug
closed
Subscribe doesn't show up in the posts 
https://github.com/quarto-dev/quarto-cli/issues/2787