blogTitle is overridden by site title when at site root

### 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.
- [ ] I have tried creating a repro with https://new.docusaurus.io.
- [X] I have read the console error message carefully (if applicable).

### Description

blogTitle not working

Someone at the end of this thread seems to have a similar issue: https://github.com/facebook/docusaurus/discussions/5119

### Reproducible demo

_No response_

### Steps to reproduce

```typescript
presets: [
[
'classic',
{
blog: {
routeBasePath: "/",
blogTitle: "Blog",
},
} satisfies Preset.Options,
],
],
```

### Expected behavior

I want the title of the page to be: "Blog | Foo"

### Actual behavior

The blogTitle is not showing, I get the config title twice: "Foo | Foo".

### Your environment

- Public source code:
- Public site URL:
- Docusaurus version used: 3.2.1
- Environment name and version (e.g. Chrome 89, Node.js 16.4):
- Operating system and version (e.g. Ubuntu 20.04.2 LTS):

### Self-service

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