Fix failing nbconvert CI test by generating a proper temp ipynb file

[IanMatthewHuff]

Fixes #11190

Working on getting branch all green for release.

• Pull request represents a single change (i.e. not fixing disparate/unrelated things in a single PR).
• Title summarizes what is changing.
• Has a news entry file (remember to thank yourself!).
• Appropriate comments and documentation strings in the code.
• Has sufficient logging.
• Has telemetry for feature-requests.
• Unit tests & system/integration tests are added/updated.
• Test plan is updated as appropriate.
• package-lock.json has been regenerated by running npm install (if dependencies have changed).

[IanMatthewHuff]

This is an invalid INotebookContent and nbconvert wasn't liking the kernel entry as it's not part of the spec.

[codecov-commenter]

Codecov Report

Merging #11191 (4a56550) into main (f0c4d6f) will decrease coverage by 0%.
The diff coverage is n/a.

@@          Coverage Diff           @@
##            main   #11191   +/-   ##
======================================
- Coverage     63%      63%   -1%     
======================================
  Files        485      485           
  Lines      34121    34121           
  Branches    5564     5564           
======================================
- Hits       21665    21651   -14     
- Misses     10398    10412   +14     
  Partials    2058     2058           

Impacted Files	Coverage Δ
...interpreter/nbconvertExportToPythonService.node.ts	76% <0%> (-18%)	⬇️
src/notebooks/debugger/debugger.ts	66% <0%> (-12%)	⬇️
.../standalone/survey/dataScienceSurveyBanner.node.ts	66% <0%> (-6%)	⬇️
...kernels/jupyter/preferredRemoteKernelIdProvider.ts	92% <0%> (-5%)	⬇️
src/notebooks/debugger/debuggingManagerBase.ts	70% <0%> (-5%)	⬇️
src/platform/common/process/baseDaemon.node.ts	50% <0%> (-4%)	⬇️
src/notebooks/debugger/kernelDebugAdapterBase.ts	76% <0%> (-2%)	⬇️
src/kernels/raw/launcher/kernelProcess.node.ts	71% <0%> (-2%)	⬇️
src/platform/msrCrypto/msrCrypto.js	16% <0%> (-1%)	⬇️
src/kernels/common/baseJupyterSession.ts	80% <0%> (+<1%)	⬆️
... and 8 more

[IanMatthewHuff]

Initial run of tests cleared the nbconvert failures, but I did see one failure with:
remote, nonConda, 3.9, desktop, ubuntu-latest - Kernel Event - Kernel Events

So trying a quick re-run to see if that is still there.