[Validator] avoid broken rendering of inline types in UniqueEntity

This PR fixes an issue in the documentation where inline type annotations like | ``string`` | were not rendering correctly due to reStructuredText interpreting the | characters as substitution references.

Changes:
Replaced | ``string`` | with a more reliable format: boolean, string or array

Ensures consistent rendering across Sphinx and other reST parsers

This improves readability and avoids confusion when displaying valid type options in inline documentation.

Author: santysisi

reference/constraints/UniqueEntity.rst

@@ -277,7 +277,7 @@ each with a single field.
 ``ignoreNull``
 ~~~~~~~~~~~~~~
 
-**type**: ``boolean`` | ``string`` | ``array`` **default**: ``true``
+**type**: ``boolean``, ``string`` or ``array`` **default**: ``true``
 
 If this option is set to ``true``, then the constraint will allow multiple
 entities to have a ``null`` value for a field without failing validation.