add release notes entry

docs/release-notes/.FSharp.Compiler.Service/9.0.200.md

@@ -12,6 +12,7 @@
 * Add warning when downcasting from nullable type to non-nullable ([PR #17965](https://github.com/dotnet/fsharp/pull/17965))
 * Fix missing nullness warning in case of method resolution multiple candidates ([PR #17917](https://github.com/dotnet/fsharp/pull/17918))
 * Fix failure to use bound values in `when` clauses of `try-with` in `seq` expressions ([# 17990](https://github.com/dotnet/fsharp/pull/17990))
+* Fix a race condition in file book keeping in the compiler service ([#18008](https://github.com/dotnet/fsharp/pull/18008))
 
 ### Added