Should filter out markdown cells from full notebook execute requests

[roblourens]

• "Run all cells"
• The kernel gets one execute request for the full notebook
• It should get ranges that do not include markdown cells

[vscode-triage-bot]

Pinging notebook topic followers: @claudiaregio @rchiodo @greazer @DonJayamanne @jilljac

[roblourens]

Executing markdown cells was causing issues in the github issues notebook

[mjbvz]

@roblourens To verify, I debugged the GitHub issues notebook extension and placed a breakpoint in executeCellsRequest. After executing run all cells, I don't see any markdown cells being included in the list of ranges

Let me know if these verification steps are incorrect

[roblourens]

Perfect, thanks!