Blocks: Resolve apiVersion browser warning

[AlexGStapleton]

This PR resolves the following warning that'll be output for all of all our blocks.

The block "sowb/widget-block" is registered with API version 2 or lower. This means that the post editor may work as a non-iframe editor. Since all editors are planned to work as iframes in the future, set the apiVersion field to 3 and test the block inside the iframe editor. See: https://developer.wordpress.org/block-editor/reference-guides/block-api/block-api-versions/#version-3-wordpress-6-3