minor symfony#8011 Update LessThan.rst "Basic Usage" part (tzfrs)

This PR was submitted for the 3.3 branch but it was merged into the 2.7 branch instead (closes symfony#8011).

Discussion
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Update LessThan.rst "Basic Usage" part

* Fix first bullet point containing information about the LessThanOrEqual constraint
* Fix second bullet point not displaying the number `80 ` in code highlighted format.

Commits
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0997d83 Update LessThan.rst "Basic Usage" part

Author: xabbuh

reference/constraints/LessThan.rst

@@ -26,8 +26,8 @@ Basic Usage
 
 The following constraints ensure that:
 
-* the number of ``siblings`` of a ``Person`` is less than or equal to ``5``
-* ``age`` is less than``80``
+* the number of ``siblings`` of a ``Person`` is less than ``5``
+* ``age`` is less than ``80``
 
 .. configuration-block::