Update to 6.3.0

• Handle early connection errors such as 421 during connection and EHLO states
• Switch to Github Actions for CI
• Generate debug output for mail(), sendmail, and qmail transports. Enable using the same mechanism as for SMTP: set SMTPDebug > 0
• Make the mail() and sendmail transports set the envelope sender the same way as SMTP does, i.e. use whatever From is set to, only falling back to the sendmail_from php.ini setting if From is unset. This avoids errors from the mail() function if Sender is not set explicitly and php.ini is not configured. This is a minor functionality change, so bumps the minor version number.
• Extend parseAddresses to decode encoded names, improve tests

Sponsored by: Netzkommune GmbH