[ci] temp fix for missing dependency on Windows (#2440)

.appveyor.yml

@@ -54,5 +54,5 @@ test_script:
         if (!$?) { $host.SetShouldExit(-1) }
       }  # run all examples
   - cd %APPVEYOR_BUILD_FOLDER%\examples\python-guide\notebooks
-  - conda install -q -y -n test-env ipywidgets notebook
+  - conda install -q -y -n test-env ipywidgets notebook pywin32
   - jupyter nbconvert --ExecutePreprocessor.timeout=180 --to notebook --execute --inplace *.ipynb  # run all notebooks

.ci/test_windows.ps1

@@ -49,6 +49,6 @@ if ($env:TASK -eq "regular") {
     python $file ; Check-Output $?
   }  # run all examples
   cd $env:BUILD_SOURCESDIRECTORY/examples/python-guide/notebooks
-  conda install -q -y -n $env:CONDA_ENV ipywidgets notebook
+  conda install -q -y -n $env:CONDA_ENV ipywidgets notebook pywin32
   jupyter nbconvert --ExecutePreprocessor.timeout=180 --to notebook --execute --inplace *.ipynb ; Check-Output $?  # run all notebooks
 }