Checkbox is no longer marked required by default for required fields, but can be configured to do so

Previously, the checkbox widget would make the checkbox required, if the underlying field was required, which means that the "On value" needed to be specified in order to successfully submit the form. This was not consistent with the meaning of a required field, which should allow either the "On value" or the "Off value" to be submitted (as long as any value is submitted). This prevented site builders and module developers from marking boolean fields as required in many cases, even though they should have been required according to the data model.

To fix this, a new setting was added to the boolean checkbox widget that determines whether or not the checkbox will be marked as required. The setting is only shown if the field itself is marked as required, and defaults to FALSE. This means that checkboxes for required fields will no longer be required by default. For existing sites this setting will be set to TRUE as part of the database update, to match the previous behavior.