Do the best to save .NET output into ipynb format

[DonJayamanne]

For #6192
Not for release, but easy fix for .NET folk (lets leave in insiders for now)

[codecov-commenter]

Codecov Report

Merging #6196 (8d1712e) into main (38d5e82) will increase coverage by 0%.
The diff coverage is 38%.

@@          Coverage Diff          @@
##            main   #6196   +/-   ##
=====================================
  Coverage     72%     72%           
=====================================
  Files        401     401           
  Lines      27028   27039   +11     
  Branches    3979    3984    +5     
=====================================
+ Hits       19519   19537   +18     
+ Misses      5860    5857    -3     
+ Partials    1649    1645    -4     

Impacted Files	Coverage Δ
src/client/datascience/notebook/helpers/helpers.ts	72% <38%> (-3%)	⬇️
...active-common/intellisense/intellisenseProvider.ts	74% <0%> (+<1%)	⬆️
src/client/datascience/jupyter/jupyterNotebook.ts	76% <0%> (+<1%)	⬆️
src/client/datascience/raw-kernel/rawSocket.ts	86% <0%> (+1%)	⬆️
src/client/datascience/notebook/integration.ts	73% <0%> (+2%)	⬆️
...rc/client/datascience/jupyter/debuggerVariables.ts	78% <0%> (+3%)	⬆️
src/client/common/process/pythonDaemonPool.ts	80% <0%> (+4%)	⬆️