minor #19020 Update target branch for feature updates to 6.4 (jnoordsij)

This PR was merged into the 5.4 branch.

Discussion
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Update target branch for feature updates to 6.4

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This is the default suggested within the GitHub repository, so I think documentation should match it.

Commits
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38c91ac Update target branch for feature updates to 6.4

Author: javiereguiluz

contributing/code/pull_requests.rst

@@ -132,7 +132,7 @@ work:
   branch (you can find them on the `Symfony releases page`_). E.g. if you
   found a bug introduced in ``v5.1.10``, you need to work on ``5.4``.
 
-* ``6.3``, if you are adding a new feature.
+* ``6.4``, if you are adding a new feature.
 
   The only exception is when a new :doc:`major Symfony version </contributing/community/releases>`
   (5.0, 6.0, etc.) comes out every two years. Because of the