text: Title: Row-wise weighted mean gives incorrect results
  Body: ### Version of Awkward Array
  
  2.6.9
  
  ### Description and code to reproduce
  
  I am doing a row-wise weighted mean in an awkward array and getting wrong results.
  
  Here's an MRE with outputs in the comments:
  
  ```python
  import awkward as ak
  
  data = ak.Array(
      [
          [1, 2, 3],
          [4, 5],
      ]
  )
  
  weight = ak.Array(
      [
          [1, 1, 2],
          [1, 10],
      ]
  )
  
  # manual row-by-row - expected results
  print(ak.mean(data[0], weight=weight[0]))  # -> 2.25
  print(ak.mean(data[1], weight=weight[1]))  # -> 4.909090909090909
  
  # manual vectorized - expected results
  weights_norm = weight / ak.sum(weight, axis=1)
  print(ak.sum(weights_norm * data, axis=1))  # -> [2.25, 4.91]
  
  # the most natural call I expected to work - incorrect result in the 2nd row
  print(ak.mean(data, weight=weight, axis=1))  # -> [2.25, 13.5]
  ```