minor #14445 Update custom_constraint.rst static::class instead of get_class($this) (AndrewCherabaev)

This PR was submitted for the 5.1 branch but it was merged into the 4.4 branch instead.

Discussion
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Update custom_constraint.rst static::class instead of get_class($this)

Usage of self::class instead of get_class($this)

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Commits
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1dee4f8 Update custom_constraint.rst

Author: wouterj

validation/custom_constraint.rst

@@ -45,7 +45,7 @@ has this default logic::
     // in the base Symfony\Component\Validator\Constraint class
     public function validatedBy()
     {
-        return \get_class($this).'Validator';
+        return static::class.'Validator';
     }
 
 In other words, if you create a custom ``Constraint`` (e.g. ``MyConstraint``),