Fix example.pass.cpp test

Author: JMazurkiewicz

libcxx/test/std/ranges/range.adaptors/range.join.with/range.join.with.overview/example.pass.cpp

@@ -20,6 +20,7 @@
 
 #include <ranges>
 
+#include <cassert>
 #include <string>
 #include <vector>
 
@@ -34,7 +35,7 @@ constexpr bool test() {
 }
 
 int main(int, char**) {
-  test();
+  assert(test());
   static_assert(test());
 
   return 0;