Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and discussions and couldn’t find anything or linked relevant results below
• I made sure the docs are up to date
• I included tests (or that’s not needed)

Description of changes

Fix the issue when used as a dependency under docusaurus

[ERROR] Client bundle compiled with errors therefore further build is impossible.
× Module not found: Can't resolve 'extend' in '/home/xxxxxxxx/.yarn/berry/cache/unified-npm-11.0.5-ac5333017e-10c0.zip/node_modules/unified/lib'
╭─[350:0]
348 │
349 │ import {bail} from 'bail'
350 │ import extend from 'extend'
· ───────────────────────────
351 │ import {ok as assert} from 'devlop'
352 │ import isPlainObj from 'is-plain-obj'
╰────
help: Did you mean '/home/xxxxxxxx/.yarn/berry/cache/extend-npm-3.0.2-e1ca07ac54-10c0.zip/node_modules/extend/index.js'?

    The request 'extend' failed to resolve only because it was resolved as fully specified,
    probably because the origin is strict EcmaScript Module,
    e. g. a module with javascript mimetype, a '*.mjs' file, or a '*.js' file where the package.json contains '"type": "module"'.
    
    The extension in the request is mandatory for it to be fully specified.
    Add the extension to the request.