Use Append for not format string

[feiyun0112]

No description provided.

[codecov]

Codecov Report

Merging #5826 (e2be0aa) into main (7c34ab9) will decrease coverage by 0.04%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main    #5826      +/-   ##
==========================================
- Coverage   68.37%   68.32%   -0.05%     
==========================================
  Files        1131     1131              
  Lines      241291   241291              
  Branches    25053    25053              
==========================================
- Hits       164993   164873     -120     
- Misses      69806    69916     +110     
- Partials     6492     6502      +10     

Flag	Coverage Δ
Debug	68.32% <0.00%> (-0.05%)	⬇️
production	62.94% <0.00%> (-0.07%)	⬇️
test	89.24% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...t.ML.FastTree/TreeEnsemble/InternalTreeEnsemble.cs	68.19% <0.00%> (ø)
src/Microsoft.ML.FastTree/Utils/Timer.cs	45.20% <0.00%> (ø)
...osoft.ML.KMeansClustering/KMeansPlusPlusTrainer.cs	83.60% <0.00%> (-7.16%)	⬇️
src/Microsoft.ML.Data/Training/TrainerUtils.cs	65.86% <0.00%> (-3.82%)	⬇️
...crosoft.ML.StandardTrainers/Standard/SdcaBinary.cs	85.49% <0.00%> (-3.08%)	⬇️
src/Microsoft.ML.Sweeper/AsyncSweeper.cs	71.42% <0.00%> (-1.37%)	⬇️
...crosoft.ML.StandardTrainers/Optimizer/Optimizer.cs	71.96% <0.00%> (-1.16%)	⬇️
...oft.ML.StandardTrainers/Standard/SdcaMulticlass.cs	91.46% <0.00%> (-1.03%)	⬇️
src/Microsoft.ML.Data/Utils/LossFunctions.cs	66.83% <0.00%> (-0.52%)	⬇️
...ML.Transforms/Text/StopWordsRemovingTransformer.cs	86.67% <0.00%> (+0.14%)	⬆️
... and 2 more

[eerhardt]

@michaelgsharp - it might be helpful to turn on more roslyn analyzers in dotnet/machinelearning so these things are checked and don't regress on new code.

[michaelgsharp]

LGTM