Clang 13: Fix build errors ...

... due to local variables only being written to (but never read).

Signed-off-by: Daniel Edwards <dev@danieledwards.de>

Gems/GraphModel/Code/Source/Model/Node.cpp

@@ -68,7 +68,7 @@ namespace GraphModel
         CreateSlotData(m_inputEventSlots, m_inputEventSlotDefinitions);
         CreateSlotData(m_outputEventSlots, m_outputEventSlotDefinitions);
 
-        int numExtendableSlots = 0;
+        [[maybe_unused]] int numExtendableSlots = 0;
         for (auto it = m_extendableSlots.begin(); it != m_extendableSlots.end(); it++)
         {
             numExtendableSlots += aznumeric_cast<int>(it->second.size());

Gems/GraphModel/Code/Source/Model/Slot.cpp

@@ -491,7 +491,7 @@ namespace GraphModel
             // multiple supported types, Slot::GetDataType() will call GetParentNode()
             // to try and resolve its type, which will be a nullptr at this point
             // because the parent won't be valid yet
-            bool valueTypeSupported = false;
+            [[maybe_unused]] bool valueTypeSupported = false;
             DataTypePtr valueDataType = GetGraphContext()->GetDataTypeForValue(m_value);
             for (DataTypePtr dataType : GetSupportedDataTypes())
             {