[Fix] add 'override' keyword to setBackend() member function in Slice.hpp

include/aidge/operator/Slice.hpp

@@ -90,7 +90,7 @@ public:
         mOutputs[0]->resize(outputDims);
     }
 
-    void setBackend(const std::string &name) {
+    void setBackend(const std::string &name) override {
         mImpl = Registrar<Slice_Op>::create(name)(*this);
         mOutputs[0]->setBackend(name);