🐛 BUG: Component slots in markdown pages throw an error

[tony-sull]

What version of @astrojs/compiler are you using?

0.14.1

What package manager are you using?

pnpm

What operating system are you using?

mac

Describe the Bug

Ran into a build error when upgrading astro.build to astro@0.26. Narrowed it down to component slots being used in two markdown pages

<!-- src/pages/blog/introducing-astro.md -->
<Blockquote>
  <Fragment slot="quote">
    A well-designed system makes it easy to do the right things and annoying (but not impossible) to do the wrong things
  </Fragment>

  <Fragment slot="cite">Jeff Atwood, <a href="https://blog.codinghorror.com/falling-into-the-pit-of-success/">Falling Into The Pit of Success</a></Fragment>
</Blockquote>

Error message

panic: Element with a slot='...' attribute must be a child of a component or a descendant of a custom element

goroutine 124 [running]:
github.com/withastro/compiler/internal/printer.render1(0x5f9b08, 0x57f860, {0x0, 0x0, 0x3, 0x0, {{0x673e40, 0x8}, {0x4b05f0, 0x4f}, ...}})
	github.com/withastro/compiler/internal/printer/print-to-js.go:409 +0x533

Link to Minimal Reproducible Example

https://github.com/withastro/astro.build/tree/chore/astro-0.26

[JuanM04]

It also happend to me with the slot being inside a conditional:

<MainLayout {...props}>
  <slot />

  {mathStyles && <link rel="stylesheet" href={mathStyles} slot="head" />}
</MainLayout>

[natemoo-re]

Ah that might be the culprit, @JuanM04! I probably won't be able to look at this for another week, but I'd really like to fix this ASAP.