minor #15529 [Form][2.7] fix a namespace in the upgrade file (craue)

This PR was merged into the 2.7 branch.

Discussion
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[Form][2.7] fix a namespace in the upgrade file

| Q             | A
| ------------- | ---
| Fixed tickets | --
| License       | MIT

Commits
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f4a785b fixed a namespace in the upgrade file

UPGRADE-2.7.md

@@ -168,7 +168,7 @@ Form
    }
    ```
 
- * `Symfony\Component\Form\Extension\Core\ChoiceList\View\ChoiceView` was
+ * `Symfony\Component\Form\Extension\Core\View\ChoiceView` was
    deprecated and will be removed in Symfony 3.0. You should use
    `Symfony\Component\Form\ChoiceList\View\ChoiceView` instead.
    The constructor arguments of the new class are in the same order than in the