minor symfony#7995 Fix typo (spbentz)

This PR was submitted for the 3.3 branch but it was merged into the 2.7 branch instead (closes symfony#7995).

Discussion
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Fix typo

Unknown "assets_version" function. Did you mean "asset_version"?

Commits
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b951ba8 Fix typo

Author: xabbuh

reference/twig_reference.rst

@@ -130,12 +130,12 @@ set for the package and the URL path. More information in
 :ref:`templating-assets`. For asset versioning, see
 :ref:`reference-framework-assets-version`.
 
-assets_version
+asset_version
 ~~~~~~~~~~~~~~
 
 .. code-block:: twig
 
-    {{ assets_version(packageName = null) }}
+    {{ asset_version(packageName = null) }}
 
 ``packageName`` *(optional)*
     **type**: ``string`` | ``null`` **default**: ``null``