fix the type of ForwardableEmailMessage (#10075)

Author: vicb

.changeset/chatty-buses-begin.md

@@ -0,0 +1,5 @@
+---
+"miniflare": patch
+---
+
+fix the type of ForwardableEmailMessage

packages/miniflare/src/workers/core/email.ts

@@ -1,5 +1,5 @@
 import assert from "node:assert";
-import { ForwardableEmailMessage } from "@cloudflare/workers-types";
+import { ForwardableEmailMessage } from "@cloudflare/workers-types/experimental";
 import { $, blue, red, reset, yellow } from "kleur/colors";
 import { LogLevel, SharedHeaders } from "miniflare:shared";
 import PostalMime, { Email } from "postal-mime";