Describe the pull request

Update mermaid-js to 11.9.0 ( main branch) because old version cant render some mermaid diagrams with modern features (see Test plan below).

Possible fix issue: #7409

Checklist

• I agree to follow the Code of Conduct by submitting this pull request.
• I have read and acknowledge the Contributing guide.
• I have added test cases to cover the new code or have provided the test plan.

Test plan

1. Create repo with README.md:

This is mermaid diagram:

```mermaid
sequenceDiagram
    Alice->>+John: Hello John, how are you?
    Alice->>+John: John, can you hear me?
    John-->>-Alice: Hi Alice, I can hear you!
    John-->>-Alice: I feel great!

    box #ffffff
    participant Alice
    end
```

Did you see it?

2. View repo in web ui
3. You should see correct rendered sequence diagram like:

sequenceDiagram
    Alice->>+John: Hello John, how are you?
    Alice->>+John: John, can you hear me?
    John-->>-Alice: Hi Alice, I can hear you!
    John-->>-Alice: I feel great!

    box #ffffff
    participant Alice
    end