fix : replaced unused var call

src/operator/Concat.cpp

@@ -25,7 +25,7 @@ void Aidge::Concat_OpImpl::forward() {
     assert(op.getInput(0) && "missing input in Concat operator");
     for (IOIndex_t i = 1; i < mOp.nbInputs(); ++i) {
         assert(op.getInput(i) && "missing input in Concat operator");
-        assert(op.getInput(i)->dataType() == datatypeFirstInput);
+        assert(op.getInput(i)->dataType() == op.getInput(0)->dataType());
     }
 
     DimSize_t outputAxisValue = 0;