Fix problem with markdown being passed to pylance

[rchiodo]

Fixes: #8769

With pylance handling intellisense, we were also passing non python cells along. This filters those out so pylance never sees them.

Before change:

Notice the off by one error on the diagnostics

After change:

[rchiodo]

No bug yet entered for this, as nobody else is using pylance yet.

[codecov-commenter]

Codecov Report

Merging #8768 (1084ebd) into main (c2bbbaa) will increase coverage by 0%.
The diff coverage is 100%.

@@          Coverage Diff          @@
##            main   #8768   +/-   ##
=====================================
  Coverage     71%     71%           
=====================================
  Files        381     381           
  Lines      24535   24536    +1     
  Branches    3772    3774    +2     
=====================================
+ Hits       17621   17631   +10     
+ Misses      5394    5382   -12     
- Partials    1520    1523    +3     

Impacted Files	Coverage Δ
...ence/notebook/intellisense/intellisenseProvider.ts	81% <100%> (+<1%)	⬆️
...lient/datascience/variablesView/notebookWatcher.ts	90% <0%> (-3%)	⬇️
src/client/datascience/raw-kernel/rawSocket.ts	84% <0%> (-1%)	⬇️
...atascience/interactive-window/interactiveWindow.ts	69% <0%> (+1%)	⬆️
src/client/datascience/dataScienceSurveyBanner.ts	75% <0%> (+6%)	⬆️