fix(nextjs): Import helper from subpath to avoid static analysis warn…

…ings

Otherwise, next prod builds will report the following issue:

A Node.js API is used (MessageEvent at line: 28) which is not supported in the Edge Runtime.
Learn more: https://nextjs.org/docs/api-reference/edge-runtime

Import trace for requested module:
./node_modules/@clerk/shared/dist/chunk-RSOCGYTF.mjs
./node_modules/@clerk/shared/dist/index.mjs

packages/nextjs/src/server/createGetAuth.ts

@@ -1,7 +1,7 @@
 import type { AuthObject } from '@clerk/backend';
 import { constants } from '@clerk/backend/internal';
 import { decodeJwt } from '@clerk/backend/jwt';
-import { isTruthy } from '@clerk/shared';
+import { isTruthy } from '@clerk/shared/underscore';
 
 import { withLogger } from '../utils/debugLogger';
 import { getAuthDataFromRequest } from './data/getAuthDataFromRequest';