ci: update error reference docs (withastro#11545)

Co-authored-by: sarah11918 <[email protected]>

Author: astrobot-houston

src/content/docs/en/reference/errors/unsupported-external-redirect.mdx

@@ -13,7 +13,7 @@ import DontEditWarning from '~/components/DontEditWarning.astro'
 <DontEditWarning />
 
 
-> **UnsupportedExternalRedirect**: An external redirect must start with http or https, and must be a valid URL.
+> **UnsupportedExternalRedirect**: The destination URL in the external redirect from "FROM" to "TO" is unsupported.
 
 ## What went wrong?
 An external redirect must start with http or https, and must be a valid URL.