Fix BCMath release announcement example (#1230)

Fixes issue php/doc-en#4466

Author: philip

releases/8.4/release.inc

@@ -346,7 +346,7 @@ PHP
                         <?php highlight_php_trimmed(
                             <<<'PHP'
 $num1 = '0.12345';
-$num2 = 2;
+$num2 = '2';
 $result = bcadd($num1, $num2, 5);
 
 echo $result; // '2.12345'