Update release notes

Author: brianrourkeboll

docs/release-notes/.FSharp.Compiler.Service/9.0.300.md

@@ -26,6 +26,7 @@
 * Fix confusing type inference error in task expression ([Issue #13789](https://github.com/dotnet/fsharp/issues/13789), [PR #18450](https://github.com/dotnet/fsharp/pull/18450))
 * Fix missing `null` highlighting in tooltips ([PR #18457](https://github.com/dotnet/fsharp/pull/18457))
 * Make `[<CallerMemberName; Struct>]` combination work([PR #18444](https://github.com/dotnet/fsharp/pull/18444/))
+* Miscellaneous unused opens analyzer fixes. ([Issue #17629](https://github.com/dotnet/fsharp/issues/17629), [Issue #17929](https://github.com/dotnet/fsharp/issues/17929), [Issue #16226](https://github.com/dotnet/fsharp/issues/16226), [Issue #18389](https://github.com/dotnet/fsharp/issues/18389), [PR #18510](https://github.com/dotnet/fsharp/pull/18510))
 
 ### Added
 * Added missing type constraints in FCS. ([PR #18241](https://github.com/dotnet/fsharp/pull/18241))