Update deep-dive-blog-posts.md (dotnet#71907)

Update deep dive blog list with Stephen Toub's Performance Improvements in .NET 6

Author: skynode

docs/deep-dive-blog-posts.md

@@ -7,6 +7,7 @@
 - [Performance improvements in .NET Core 2.1](https://devblogs.microsoft.com/dotnet/performance-improvements-in-net-core-2-1/)
 - [Performance improvements in .NET Core 3.0](https://devblogs.microsoft.com/dotnet/performance-improvements-in-net-core-3-0/)
 - [Performance improvements in .NET 5](https://devblogs.microsoft.com/dotnet/performance-improvements-in-net-5/)
+- [Performance improvements in .NET 6](https://devblogs.microsoft.com/dotnet/performance-improvements-in-net-6/)
 
 
 ### Posts that take a high-level look at the entire source: