[test] Require asserts for pullback_generation_nested_addelement_adjoints.swift

It looks like `--debug-only` requires an asserts build

Author: hamishknight

test/AutoDiff/SILOptimizer/pullback_generation_nested_addelement_adjoints.swift

@@ -1,5 +1,8 @@
 // RUN: %target-swift-frontend -emit-sil -verify -Xllvm --sil-print-after=differentiation -Xllvm --debug-only=differentiation %s 2>&1 | %FileCheck %s
 
+// Needed for '--debug-only'
+// REQUIRES: asserts
+
 import _Differentiation
 
 //===----------------------------------------------------------------------===//
@@ -138,4 +141,4 @@ func multipleExtractionsFromSameStruct(_ model: SmallTestModel) -> Float{
 // CHECK:   dealloc_stack %11 : $*SmallTestModel.TangentVector 
 // CHECK:   debug_value %39 : $SmallTestModel.TangentVector, let, name "model", argno 1 
 // CHECK:   return %39 : $SmallTestModel.TangentVector      
-// CHECK: }
+// CHECK: }