Previous refactoring renamed the "data-type" attribute of widget markup
containers to "data-widget", breaking the "unique" validator as it relies
on it to lookup options.
Fixes: #3341
Fixes: 13e9e3e9e ("treewide: fix "Unhandled token" errors with Lua CBI maps")
Signed-off-by: Jo-Philipp Wich <jo@mein.io>