Fix falcon with SDPA, alibi but no passed mask #30123
                
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As per title, fixes #29946
There was a (minor) bug in #26572, where if an user uses a Falcon model with alibi and SDPA, but not passing
attention_maskinput, theattn_maskargument passed to SDPA would not be causal (as it use to be (see here and here). I likely misunderstood something at the time.I think this bug was not catched in the CI because Falcon tests do not test Alibi thoroughly.