minor #30064 [Form][MappingRule] Remove unnecessary cast (fancyweb)

This PR was merged into the 3.4 branch.

Discussion
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[Form][MappingRule] Remove unnecessary cast

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Commits
-------

fc09c28 [Form][MappingRule] Remove unnecessary cast

src/Symfony/Component/Form/Extension/Validator/ViolationMapper/MappingRule.php

@@ -55,7 +55,7 @@ public function getOrigin()
      */
     public function match($propertyPath)
     {
-        if ($propertyPath === (string) $this->propertyPath) {
+        if ($propertyPath === $this->propertyPath) {
             return $this->getTarget();
         }
     }