unbiased=False for torch.var_mean path of ConvNeXt LN. Fix #1090

Author: rwightman

timm/models/convnext.py

@@ -94,7 +94,7 @@ def forward(self, x) -> torch.Tensor:
             return F.layer_norm(
                 x.permute(0, 2, 3, 1), self.normalized_shape, self.weight, self.bias, self.eps).permute(0, 3, 1, 2)
         else:
-            s, u = torch.var_mean(x, dim=1, keepdim=True)
+            s, u = torch.var_mean(x, dim=1, unbiased=False, keepdim=True)
             x = (x - u) * torch.rsqrt(s + self.eps)
             x = x * self.weight[:, None, None] + self.bias[:, None, None]
             return x