fix pack issue with readmes and snupkgs

[zkat]

Bug

Fixes: NuGet/Home#10791

Regression? No

Description

According to NuGet.org symbol package constraints, the symbol package should not have the readme file.
So this PR:

1. skip validation of readme file if the package is a symbol package
2. add a test for packing snupkgs with readme file, and verify it's successfully created the snupkgs.

PR Checklist

• PR has a meaningful title

• PR has a linked issue.

• Described changes

• Tests

  • Automated tests added
  • OR
  • Test exception
  • OR
  • N/A

• Documentation

  • Documentation PR or issue filled
  • OR
  • N/A

[jeffkl]

I'm not sure why this is commented out?

[heng-liu]

Thanks for reviewing! Reverted.

[jeffkl]

We need a unit test that would have caught the fact that the functionality is broken.

[heng-liu]

We need a unit test that would have caught the fact that the functionality is broken.

Thanks! Added.

[jeffkl]

🥇

[heng-liu]

Hi @aortiz-msft , pls approve this PR if it's good to merge. Thanks!

[zivkan]

Edit: Apparently I didn't get enough sleep. All's good.

[aortiz-msft]

Could you please the PR description? I don't think that "This does the stuff over at NuGet/Home#10791 (comment)" is entirely accurate.

[heng-liu]

Hi @aortiz-msft , thanks for the suggestion! Updated the description in the PR.

[RehanSaeed]

Any ideas when this will roll out? .NET Core 6?

[loic-sharma]

This should be in .NET 6 RC2 which will be released in a few weeks.