minor symfony#2402 [LiveComponent] Fix variable in docs (xDeSwa)

This PR was squashed before being merged into the 2.x branch.

Discussion
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[LiveComponent] Fix variable in docs

I think it's a wrong variable

Commits
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f39ab6f [LiveComponent] Fix variable in docs

src/LiveComponent/doc/index.rst

@@ -2741,7 +2741,7 @@ name with ``#[LiveArg]`` in front::
     public function incrementProductCount(#[LiveArg] int $product)
     {
         $this->productCount++;
-        $this->lastProduct = $data['product'];
+        $this->lastProductId = $product;
     }
 
 And because event listeners are also actions, you can type-hint an argument