try this

sites/svelte.dev/placeholder/index.html

@@ -0,0 +1 @@
+<p>see <a href="https://github.com/sveltejs/svelte/pull/9424">#9424</a></p>

sites/svelte.dev/vercel.json

@@ -3,5 +3,6 @@
 	"github": {
 		"silent": true
 	},
-	"buildCommand": "echo \"TODO reinstate in future: cd ../../packages/svelte && pnpm prepublishOnly && cd ../../sites/svelte.dev && pnpm rebuild sharp && pnpm build\""
+	"buildCommand": "echo \"TODO reinstate in future: cd ../../packages/svelte && pnpm prepublishOnly && cd ../../sites/svelte.dev && pnpm rebuild sharp && pnpm build\"",
+	"outputDirectory": "placeholder"
 }