minor #15778 Update upload_file.rst (sfmok)

This PR was submitted for the 5.3 branch but it was merged into the 5.4 branch instead.

Discussion
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Update upload_file.rst

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Commits
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0f437c0 Update upload_file.rst

Author: javiereguiluz

controller/upload_file.rst

@@ -199,7 +199,7 @@ There are some important things to consider in the code of the above controller:
 #. A well-known security best practice is to never trust the input provided by
    users. This also applies to the files uploaded by your visitors. The ``UploadedFile``
    class provides methods to get the original file extension
-   (:method:`Symfony\\Component\\HttpFoundation\\File\\UploadedFile::getExtension`),
+   (:method:`Symfony\\Component\\HttpFoundation\\File\\UploadedFile::getClientOriginalExtension`),
    the original file size (:method:`Symfony\\Component\\HttpFoundation\\File\\UploadedFile::getSize`)
    and the original file name (:method:`Symfony\\Component\\HttpFoundation\\File\\UploadedFile::getClientOriginalName`).
    However, they are considered *not safe* because a malicious user could tamper