Extend the unknown-attributes warning workaround to ROOT 6.24
In !2912 (merged) @chasse added a protection against a warning from cling for ROOT 6.22, but the problem is still present in ROOT 2.64 (LCG 100).
In !2912 (merged) @chasse added a protection against a warning from cling for ROOT 6.22, but the problem is still present in ROOT 2.64 (LCG 100).