Ensure all excluded files in _routes.json start with / (#6952)

* Ensure all excluded files in routes.json start with /

* fix changeset

Author: Rich-Harris

.changeset/orange-rocks-return.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/adapter-cloudflare': patch
+---
+
+Ensure all excluded paths in `_routes.json` start with /

packages/adapter-cloudflare/index.js

@@ -87,7 +87,8 @@ function get_routes_json(app_dir, assets) {
 				// We do want to show an example of a _routes.json that
 				// excludes more than just /_app/immutable/*, and favicons
 				// are a reasonable choice
-				.filter((filePath) => filePath.includes('favicon'))
+				.filter((file) => file.startsWith('favicon'))
+				.map((file) => `/${file}`)
 		]
 	};
 }