minor #18588 fix reference (xabbuh)

This PR was merged into the 6.3 branch.

Discussion
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fix reference

Commits
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db2af1f fix reference

Author: javiereguiluz

frontend/asset_mapper.rst

@@ -289,7 +289,7 @@ Preloading and Initializing "app.js"
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 In addition to the importmap, the ``{{ importmap() }}`` Twig function also renders
-an `ES module shim`_ (see the :ref:`config-importmap-polyfill <polyfill config>`) and
+an `ES module shim`_ (see the :ref:`polyfill config <config-importmap-polyfill>`) and
 a few other things, like a set of "preloads":
 
 .. code-block:: html