v6.0.0

First release of the 6.x line: Symfony 6.4, PHP 8.1 or later. Bug fixes only from now on.

Changes:

• Support only Symfony 6.4 on the 6.x branch (#108)
• Return null from getOption() for a missing key on 6.x (#109)
• Analyse 6.x with PHPStan for PHP 8.1 (#116)
• Answer 400 instead of 500 for invalid calendar query parameters (#117)
• Throw JsonException when events cannot be encoded (#118)
• Test every PHP version Symfony 6.4 supports on 6.x (#123)
• Analyse 6.x with PHPStan at max level with strict rules (#124)
• Run mutation tests with Infection on 6.x (#125)
• Declare the packages the 6.x code uses and drop unused ones (#126)
• Answer 400 instead of 500 when start or end is not a date on 6.x (#127)
• Install with --no-blocking in the 6.x CI workflow (#133)