[PHP 8.2] Fix deprecated ${var} string interpolation patterns (#42520)

PHP 8.2 deprecates string interpolation patterns that place the
dollar sign outside the curly braces. This fixes such patterns
by replacing them with proper curly braced patterns.

Fixes `Illuminate\Cookie\Middleware\EncryptCookies::validateArray()`
This is so far the only such occurrence.

Reference:
 - [PHP.Watch: `${var}` string interpolation deprecated](https://php.watch/versions/8.2/$%7Bvar%7D-string-interpolation-deprecated)
 - [wiki.php.net RFC](https://wiki.php.net/rfc/deprecate_dollar_brace_string_interpolation)

Author: Ayesh

src/Illuminate/Cookie/Middleware/EncryptCookies.php

@@ -118,7 +118,7 @@ protected function validateArray(string $key, array $value)
         $validated = [];
 
         foreach ($value as $index => $subValue) {
-            $validated[$index] = $this->validateValue("${key}[${index}]", $subValue);
+            $validated[$index] = $this->validateValue("{$key}[{$index}]", $subValue);
         }
 
         return $validated;