unfetch@5.0.0 published package might be missing files

Hi. First, thank you for this package!

I seem to be getting a strange error in version 5.0.0 that I'm not getting when I downgrade to 4.2.0. Essentially:

Version 5.0.0:

> Welcome to Node.js v18.13.0.
> Type ".help" for more information.
> \> require('./node_modules/unfetch/dist/unfetch.js')
> [Function (anonymous)]
> \> require('unfetch')
> Uncaught:
> Error: Cannot find module '/repos/.ergodark/xunn.at/node_modules/unfetch/index.js'
> at createEsmNotFoundErr (node:internal/modules/cjs/loader:1060:15)
> at finalizeEsmResolution (node:internal/modules/cjs/loader:1053:15)
> at resolveExports (node:internal/modules/cjs/loader:538:14)
> at Module._findPath (node:internal/modules/cjs/loader:607:31)
> at Module._resolveFilename (node:internal/modules/cjs/loader:1025:27)
> at Module._load (node:internal/modules/cjs/loader:885:27)
> at Module.require (node:internal/modules/cjs/loader:1105:19)
> at require (node:internal/modules/cjs/helpers:103:18) {
> code: 'MODULE_NOT_FOUND',
> path: '/repos/.ergodark/xunn.at/node_modules/unfetch/package.json'
> }

Version 4.2.0:
> Welcome to Node.js v18.13.0.
> Type ".help" for more information.
> \> require('./node_modules/unfetch/dist/unfetch.js')
> [Function (anonymous)]
> \> require('unfetch')
> [Function (anonymous)]

使用已发布的 5.0.0 版本，通过 require('unfetch') 重现该失败，然后检查其 package.json，并将打包的文件与 4.2.0 版本进行比较，包括 dist/unfetch.js 和缺失的 index.js 路径。已完成的标准是：已发布的包能够通过 require('unfetch') 成功解析，并包含其包元数据所引用的文件。

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