Fix fourslash Tests

Author: graphemecluster

src/harness/fourslashInterfaceImpl.ts

@@ -1168,6 +1168,7 @@ namespace FourSlashInterface {
             typeEntry("Partial"),
             typeEntry("Required"),
             typeEntry("Readonly"),
+            typeEntry("Writable"),
             typeEntry("Pick"),
             typeEntry("Record"),
             typeEntry("Exclude"),