make TypeWithToString private inside the shared pack

Author: erik-krogh

shared/util/codeql/util/Either.qll

@@ -1,7 +1,7 @@
 /** Provides a module for constructing a union `Either` type. */
 
 /** A type with `toString`. */
-signature class TypeWithToString {
+private signature class TypeWithToString {
   string toString();
 }
 

shared/util/codeql/util/Option.qll

@@ -1,7 +1,7 @@
 /** Provides a module for constructing optional versions of types. */
 
 /** A type with `toString`. */
-signature class TypeWithToString {
+private signature class TypeWithToString {
   string toString();
 }