Update FSComp.txt (#9556)

Author: cartermp

src/fsharp/FSComp.txt

@@ -1512,4 +1512,4 @@ featureFixedIndexSlice3d4d,"fixed-index slice 3d/4d"
 featureAndBang,"applicative computation expressions"
 featureNullableOptionalInterop,"nullable optional interop"
 featureDefaultInterfaceMemberConsumption,"default interface member consumption"
-featureWitnessPassing,"witness passing"
+featureWitnessPassing,"witness passing for trait constraints in F# quotations"