[Docusaurus v3.4] index.html in static directory raises "Multiple assets emit different content to the same filename" error

### 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.
- [X] I have read the console error message carefully (if applicable).

### Description

Using `docusaurus start` while having a `index.html` in the `static` directory will cause the following error:

`Conflict: Multiple assets emit different content to the same filename index.html`

### Reproducible demo

https://codesandbox.io/p/devbox/kind-khorana-zg4f99?file=%2Fstatic%2Findex.html%3A5%2C8

### Steps to reproduce

1. Delete index.tsx in src/page
2. create a `index.html` in the root of the `static` directory
3. Observe failure

### Expected behavior

For the html file to be added to the build like before this update, and to be able to serve a index.html file as the landing page.

### Actual behavior

Error mentioned above occurs.

### Your environment

_No response_

### Self-service

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