copilot-instructions: prefer async over task

The former is idiomatic F#, the latter is more for C#
interoperability.

Author: knocte

.github/copilot-instructions.md

@@ -2,7 +2,7 @@ We prefer the latest F# 9 features over the old syntax
 
 Prefer `voption` over `option`
 
-Prefer `task` CE over `async` CE
+Prefer `async` CE over `task` CE
 
 This is how you define a non-default F# class constructor:
 ```fsharp