minor symfony#19158 Update doctrine.rst (BooleanType)

This PR was merged into the 6.3 branch.

Discussion
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Update doctrine.rst

I think the code is about the product and the `Product` is better suited here.

Commits
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6e8fd5f Update doctrine.rst

Author: xabbuh

doctrine.rst

@@ -691,15 +691,15 @@ will automatically fetch them::
      * Fetch via primary key because {id} is in the route.
      */
     #[Route('/product/{id}')]
-    public function showByPk(Post $post): Response
+    public function showByPk(Product $product): Response
     {
     }
 
     /**
      * Perform a findOneBy() where the slug property matches {slug}.
      */
     #[Route('/product/{slug}')]
-    public function showBySlug(Post $post): Response
+    public function showBySlug(Product $product): Response
     {
     }