Vulnerable Newtonsoft.Json dependency

Please fix the reference to vulnerable `Newtonsoft.Json` versions, which cause build warnings/errors when building on .NET 9:

```
Package 'Newtonsoft.Json' 11.0.1 has a known high severity vulnerability, https://github.com/advisories/GHSA-5crp-9r3c-p9vr

[net9.0]
│
├─ Hangfire.AspNetCore (v1.8.15)
│ └─ Hangfire.NetCore (v1.8.15)
│ └─ Hangfire.Core (v1.8.15)
│ └─ Newtonsoft.Json (v11.0.1)
├─ Hangfire.Core (v1.8.15)
│ └─ Newtonsoft.Json (v11.0.1)
└─ Hangfire.SqlServer (v1.8.15)
└─ Hangfire.Core (v1.8.15)
└─ Newtonsoft.Json (v11.0.1)
```

Inspect the project dependency references for Newtonsoft.Json and reproduce the reported build on .NET 9. The issue is done when the vulnerable 11.0.1 reference is no longer resolved and the build warnings or errors shown here are gone.

Written by the indexing model from the issue text.