release: bump version to 4.0.0-beta.0#733

maribethb wants to merge 1 commit intoRaspberryPiFoundation:add-screen-reader-support-experimentalRaspberryPiFoundation/blockly-keyboard-experimentation:add-screen-reader-support-experimentalfrom

maribethb:sr-betamaribethb/blockly-keyboard-experimentation:sr-betaCopy head branch name to clipboard