Update setup.rst to mention about Intl extension

Without the Intl extension, `composer install` will face a PHP fatal error

Author: amirhosseindz

setup.rst

@@ -15,7 +15,7 @@ Technical Requirements
 Before creating your first Symfony application you must:
 
 * Install PHP 8.2 or higher and these PHP extensions (which are installed and
-  enabled by default in most PHP 8 installations): `Ctype`_, `iconv`_,
+  enabled by default in most PHP 8 installations): `Intl`_, `Ctype`_, `iconv`_,
   `PCRE`_, `Session`_, `SimpleXML`_, and `Tokenizer`_;
 * `Install Composer`_, which is used to install PHP packages.