move dotnet pipeline to the root of workflow

[LittleLittleCloud]

Why are these changes needed?

This PR moves all dotnet-related workflow to the root folder of workflow because GitHub doesn't support workflow under a subfolder of workflow

• https://docs.github.com/en/actions/using-workflows/reusing-workflows#creating-a-reusable-workflow

Related issue number

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://microsoft.github.io/autogen/docs/Contribute#documentation to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (c80df8a) 30.74% compared to head (4f35229) 30.74%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1116   +/-   ##
=======================================
  Coverage   30.74%   30.74%           
=======================================
  Files          30       30           
  Lines        4033     4033           
  Branches      913      913           
=======================================
  Hits         1240     1240           
  Misses       2714     2714           
  Partials       79       79           

Flag	Coverage Δ
unittests	30.69% <ø> (ø)

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[ekzhu]

I think you meant a subfolder of "workflows" not ".workflows". I edited the PR description .