Broken links on 'What's new in C# 14'

[davecallanbp]

Describe the issue or suggestion

Hi, there looks like two broken links in the user defined compound assignment section of the what's new in C# 14 page: https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-14#user-defined-compound-assignment

I'm guessing the underlying URLs changed.

[BillWagner]

Fixed in #47871