fix(discord): bridge undici multipart types

extensions/discord/src/client.proxy.test.ts

@@ -151,7 +151,7 @@ describe("createDiscordRestClient proxy support", () => {
         }
         const rest = createDiscordRequestClient("test-token", {
           baseUrl: `http://127.0.0.1:${address.port}`,
-          fetch: undiciFetch as typeof fetch,
+          fetch: undiciFetch as unknown as typeof fetch,
           queueRequests: false,
         });
         void rest

extensions/discord/src/proxy-request-client.ts

@@ -301,7 +301,7 @@ class ProxyRequestClientCompat {
         files: undefined,
       };
       formData.append("payload_json", JSON.stringify(cleanedBody));
-      body = formData;
+      body = formData as unknown as BodyInit;
     } else if (data?.body != null) {
       headers.set("Content-Type", "application/json");
       body = data.rawBody ? (data.body as BodyInit) : JSON.stringify(data.body);