push example: build with the release configuration

[freddyrios]

the push line expects a release build

Why:

Fixes broken example where publish fails to find the built files

What's being changed:

The dotnet build line was missing the "--configuration Release". Without that, this pattern fails to find any file "/bin/Release/.nupkg".
- run: dotnet build --configuration Release
- name: Create the package
run: dotnet pack --configuration Release
- name: Publish the package to GPR
run: dotnet nuget push /bin/Release/.nupkg

Check off the following:

• I have reviewed my changes in staging. (look for the deploy-to-heroku link in your pull request, then click View deployment)
• For content changes, I have reviewed the localization checklist
• For content changes, I have reviewed the Content style guide for GitHub Docs.

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[janiceilene]

@freddyrios Thanks so much for opening a PR! I'll get this triaged for review ⚡

[github-actions]

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