The two observer tokens carried an isolation annotation the compiler
reported as having no effect, while rejecting the plain `nonisolated` it
suggested in its place. Both follow from `@Observable`: the macro rewrites
stored properties into computed accessors, where `unsafe` means nothing
and `nonisolated` is not allowed at all.
They are notification tokens, written on the main actor and read once in
deinit. Nothing renders them, so nothing should be tracking them. Marking
them ignored lets the annotation apply to a real stored property again
and settles the warning by removing the reason it appeared.
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