COMP: Fix missing initialization braces warning

Fix missing initialization braces warning.

Fixes:
```

[CTest: warning matched]
/Users/builder/externalModules/Filtering/DisplacementField/test/itkDisplacementFieldJacobianDeterminantFilterTest.cxx:169:49:
warning: suggest braces around initialization of subobject [-Wmissing-braces]
    typename FilterType::WeightsType weights{ { 1.0, 2.0, 3.0 } };
                                                ^~~~~~~~~~~~~
                                                {            }
```

Raised for example in:
https://open.cdash.org/viewBuildError.php?type=1&buildid=7679172

Author: jhlegarreta

Modules/Filtering/DisplacementField/test/itkDisplacementFieldJacobianDeterminantFilterTest.cxx

@@ -166,7 +166,7 @@ itkDisplacementFieldJacobianDeterminantFilterTest(int, char *[])
     filter->Print(std::cout);
 
     // Run the test again with specified weights
-    typename FilterType::WeightsType weights{ { 1.0, 2.0, 3.0 } };
+    typename FilterType::WeightsType weights{ { { 1.0, 2.0, 3.0 } } };
     filter->SetDerivativeWeights(weights);
     ITK_TEST_SET_GET_VALUE(weights, filter->GetDerivativeWeights());