minor #18241 [DependencyInjection] Fix syntax in code example with promoted attribute (jeremyjumeau)

This PR was merged into the 6.2 branch.

Discussion
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[DependencyInjection] Fix syntax in code example with promoted attribute

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Commits
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93d4c89 Fix syntax in code example with promoted attribute

Author: javiereguiluz

service_container/service_decoration.rst

@@ -153,7 +153,8 @@ automatically changed to ``'.inner'``):
         class DecoratingMailer
         {
             public function __construct(
-                private #[MapDecorated] $inner,
+                #[MapDecorated]
+                private $inner,
             ) {
             }