404 Error for Translated Versioned Index Document

### Have you read the Contributing Guidelines on issues?

- [x] I have read the [Contributing Guidelines on issues](https://github.com/facebook/docusaurus/blob/main/CONTRIBUTING.md#issues).

### Prerequisites

- [x] I'm using the latest version of Docusaurus.
- [x] I have tried the `npm run clear` or `yarn clear` command.
- [x] I have tried `rm -rf node_modules yarn.lock package-lock.json` and re-installing packages.
- [x] I have tried creating a repro with https://new.docusaurus.io.
- [ ] I have read the console error message carefully (if applicable).

### Description

For the explanation, it's sufficient to assume that there's only one document, `index.mdx`, located under `/docs`. I have versioned this document for versions `1.0.0` and `2.0.0`. Version `2.0.0` represents the `current` version. Additionally, `/docs` also represents the `next` version. My documentation is also internationalized into `de`, alongside the default `en`.

With this setup, the document should be accessible in English at `/1.0.0`, `/`, and `/next`, and in German at `/de/1.0.0`, `/de`, and `/de/next`. All these paths correctly serve the corresponding document after running npm run build and npm run serve, except for `/de/1.0.0`, which returns a 404 error.

While searching for the cause of this issue, I noticed the following:

- If I add another versioned and internationalized document `intro.mdx` to `/docs`, it is correctly served under `/de/1.0.0/intro` after running `npm run build` and `npm run serve`.

- When I run `npm run start -- --locale de`, the document is correctly served on every path.

- If I rename the version `1.0.0` to `abc`, the document is correctly served on all paths after `npm run build` and `npm run serve`.

- If I add another versioned and internationalized document `index.mdx` in `/docs/tutorial`, this one is also not accessible under `/de/1.0.0/tutorial` after `npm run build` and `npm run serve`.

### Reproducible demo

https://github.com/LuggaLugga/docusaurus-bug-demo

### Steps to reproduce

1. Build the demo with `npm run build`
2. Run the demo with `npm run serve`
3. Navigate to http://localhost:3000/de/1.0.0

### Expected behavior

I expect the document from `i18n/de/docusaurus-plugin-content-docs/version-1.0.0/index.mdx` to be rendered.

### Actual behavior

The document from `i18n/de/docusaurus-plugin-content-docs/version-1.0.0/index.mdx` is not accessible according to the 404 error code.

### Your environment

- Public source code: https://github.com/LuggaLugga/docusaurus-bug-demo
- Public site URL: none
- Docusaurus version used: 3.7.0
- Environment name and version (e.g. Chrome 89, Node.js 16.4): Safari 18.04, Node 22.14.0
- Operating system and version (e.g. Ubuntu 20.04.2 LTS): macOS Sequoia 15.4

### Self-service

- [ ] I'd be willing to fix this bug myself.