Version 2.28.2

• Wrap OpenSSL command run on a try/catch block to throw a OpenSSLException exception.
• Refactor certificate downloader test helper. Now it uses Curl instead of native PHP. It was failing on PHP 7.3.
• Remove old dependencies for ReadTheDocs: mkdocs:1.2.3 and jinja2<3.1.0. Thanks to @dependabot.
• On build workflow:
  • Simplify "on" section.
  • Use php-version matrix value as singular.