fix: work around rspack warning

[vegerot]

Building Rspack projects with i18next-node-fs-backend shows this warning:

warn    Build warning: 
File: /Users/bytedance/workspace/code.byted.org/i18n_ecom_fe/i18n_ecom_shop/node_modules/.pnpm/i18next-node-fs-backend@2.1.3/node_modules/i18next-node-fs-backend/lib/index.js:1:1
  ⚠ Critical dependency: the request of a dependency is an expression
    ╭─[54:25]
 52 │   if (/^\.(js|ts)$/.test(extension)) {
 53 │     try {
 54 │       var file = require(filename);
    ·                          ─────────
 55 │       result = file.default ? file.default : file;
 56 │ 
    ╰────

 @ ../../node_modules/.pnpm/i18next-node-fs-backend@2.1.3/node_modules/i18next-node-fs-backend/index.js

This comes from Rspack in https://github.com/web-infra-dev/rspack/blob/95ba587bc379dc5ae98bfd2fdcc9d81a866ab2cd/crates/rspack_plugin_javascript/src/visitors/dependency/context_dependency_helper.rs#L212

This commit works around this warning by wrapping it in a string.

Checklist

• only relevant code is changed (make a diff before you submit the PR)
• run tests npm run test
• tests are included
• commit message and code follows the Developer's Certification of Origin

Checklist (for documentation change)

• only relevant documentation part is changed (make a diff before you submit the PR)
• motivation/reason is provided
• commit message and code follows the Developer's Certification of Origin