README: fix version badge

Looks like the version badge via Packagist does not respect the default setting of not including pre-releases.

Fixed now by letting the badge retrieve the version via the GitHub API.

The bug has been reported to shields.io: badges/shields 11127

Author: jrfnl

README.md

@@ -2,7 +2,7 @@
 
 <div aria-hidden="true">
 
-[![Latest Stable Version](https://img.shields.io/packagist/v/squizlabs/php_codesniffer?label=Stable)](https://github.com/PHPCSStandards/PHP_CodeSniffer/releases)
+[![Latest Stable Version](https://img.shields.io/github/v/release/PHPCSStandards/PHP_CodeSniffer?label=Stable)](https://github.com/PHPCSStandards/PHP_CodeSniffer/releases)
 [![Validate](https://github.com/PHPCSStandards/PHP_CodeSniffer/actions/workflows/validate.yml/badge.svg?branch=master)](https://github.com/PHPCSStandards/PHP_CodeSniffer/actions/workflows/validate.yml)
 [![Test](https://github.com/PHPCSStandards/PHP_CodeSniffer/actions/workflows/test.yml/badge.svg?branch=master)][GHA-test]
 [![Coverage Status](https://coveralls.io/repos/github/PHPCSStandards/PHP_CodeSniffer/badge.svg?branch=master)](https://coveralls.io/github/PHPCSStandards/PHP_CodeSniffer?branch=master)