Fix the added_proj_bias default value (#8800)

checking

Author: sayakpaul

src/diffusers/models/attention_processor.py

@@ -103,7 +103,7 @@ def __init__(
         cross_attention_norm_num_groups: int = 32,
         qk_norm: Optional[str] = None,
         added_kv_proj_dim: Optional[int] = None,
-        added_proj_bias: Optional[bool] = None,
+        added_proj_bias: Optional[bool] = True,
         norm_num_groups: Optional[int] = None,
         spatial_norm_dim: Optional[int] = None,
         out_bias: bool = True,