Fix circular dependency in BoostedJetTaggers

Thomas Streblerrequested to merge
tstreble/athena:CircularBoostedJetTaggers into main

Some decorations were both assigned a ReadDecorHandle and a WriteDecorHandle in some BoostedJetTaggers algorithms, triggering some circular dependency warning. Fixing those by only defining a WriteDecorHandle and using a ConstAccessor within the algorithms.

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