minor #18455 Fix incorrect placement of is_empty_callback (janklan)

This PR was submitted for the 6.3 branch but it was merged into the 5.4 branch instead.

Discussion
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Fix incorrect placement of `is_empty_callback`

I think the `is_empty_callback` placement is wrong in [6.3 docs](https://symfony.com/doc/current/reference/forms/types/form.html#empty-data). This PR fixes it.

![image](https://github.com/symfony/symfony-docs/assets/5463371/88af4062-a8ee-4132-ac93-83d3fb154ac7)

Commits
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77c98fe Fix incorrect placement of is_empty_callback

Author: OskarStark

reference/forms/types/form.rst

@@ -61,16 +61,17 @@ The actual default value of this option depends on other field options:
 * If ``data_class`` is not set and ``compound`` is ``false``, then ``''``
   (empty string).
 
+.. include:: /reference/forms/types/options/empty_data_description.rst.inc
+
+.. _reference-form-option-error-bubbling:
+
 ``is_empty_callback``
 ~~~~~~~~~~~~~~~~~~~~~
 
 **type**: ``callable`` **default**: ``null``
 
 This callable takes form data and returns whether value is considered empty.
 
-.. include:: /reference/forms/types/options/empty_data_description.rst.inc
-
-.. _reference-form-option-error-bubbling:
 
 .. include:: /reference/forms/types/options/error_bubbling.rst.inc