doesn't report checkboxes that are always checked

[airtonix]

If a Pr is built from a template, and that template starts any checkbox off as checked, then this action will only return those checkbox items if they are changed.

this action should probably change the output from

outputs = { checked, unchecked }

to

outputs = {
  changed: { checked, unchecked },
  checked, unchecked
}

so that it properly communicates the intent of the `getDiff` outputs.