test, bench: make prevector and checkqueue swap member functions noexcept

Reason:
A swap must not fail; when a class has a swap member function, it should be declared noexcept.
https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#c84-a-swap-function-must-not-fail

src/test/fuzz/checkqueue.cpp

@@ -26,7 +26,7 @@ struct DumbCheck {
         return result;
     }
 
-    void swap(DumbCheck& x)
+    void swap(DumbCheck& x) noexcept
     {
     }
 };