Update dependency x-transformers to v1.40.8 (#733)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

pyproject.toml

@@ -55,7 +55,7 @@ dependencies = [
     "diffusers==0.31.0", # Diffusion models published on Hugging Face
     "timm==1.0.11", # Image models
     "datasets==3.0.2", # Datasets published on Hugging Face
-    "x-transformers==1.40.6", # Transformer utils
+    "x-transformers==1.40.8", # Transformer utils
     "mambapy==1.2.0", # Mamba
     "denoising-diffusion-pytorch==2.1.1", # Diffusion models
     "vector-quantize-pytorch==1.18.5", # Vector quantization utils