Description:
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PHP 7.4 deprecated array and string offset access with curly braces but it also affect property name concatenation.

Test script:
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<?php

class Foo {
  public function __construct() {
    $bar = "bar";
    $this->{'foo_' . $bar} = true; // Works
    $this->foo_{$bar} = true; // Triggers Array and string offset access syntax with curly braces is deprecated
  } 
}