Use stable_sort to preserve test order (#11877)

Using sort results in a possibly-modified sorting
when all elements are "tied" - use stable_sort instead
to preserve the original ordering of tied elements.

Source/CTest/cmCTestMultiProcessHandler.cxx

@@ -484,7 +484,7 @@ void cmCTestMultiProcessHandler::CreateTestCostList()
     }
 
   TestComparator comp(this);
-  std::sort(SortedTests.begin(), SortedTests.end(), comp);
+  std::stable_sort(SortedTests.begin(), SortedTests.end(), comp);
 }
 
 //---------------------------------------------------------