Update release notes with actual PR number

Author: bbatsov

docs/release-notes/.FSharp.Core/10.0.300.md

@@ -1,6 +1,6 @@
 ### Fixed
 
-* `Seq.empty` now uses `System.Linq.Enumerable.Empty<'T>()` instead of an internal DU, fixing serialization issues with JSON.NET, STJ, and ASP.NET ObjectResult. ([Issue #17864](https://github.com/dotnet/fsharp/issues/17864), [PR #NNNN](https://github.com/dotnet/fsharp/pull/NNNN))
+* `Seq.empty` now uses `System.Linq.Enumerable.Empty<'T>()` instead of an internal DU, fixing serialization issues with JSON.NET, STJ, and ASP.NET ObjectResult. ([Issue #17864](https://github.com/dotnet/fsharp/issues/17864), [PR #19322](https://github.com/dotnet/fsharp/pull/19322))
 
 ### Added