Upgrade dotnet cli to 2.1.503

[tmat]

This is needed to get new NuSpec licensing features. See #2003 for details.

[tmat]

@dagood Ok to update to 2.1.600?

[dagood]

Source-build doesn't have a v2.1.600-SDK tag, so as far as I know, can't do this update yet. @dseefeld @crummel @dleeapho in case I'm missing something. I'm not familiar with this SDK release in particular.

[dagood]

Wait, I missed that this is an Arcade master PR... why is 2.1.600 desired rather than a 3.0.100 preview?

[tmat]

We can't use 3.0 everywhere yet. Repos are not ready.

[tmat]

Would 2.1.503 work?

[dagood]

Yeah, there are tags for 2.1.503 and even 504 and 505 SDKs on https://github.com/dotnet/source-build.

[dagood]

And actually even more directly, source-build is using the 2.1.503 toolset itself: https://github.com/dotnet/source-build/blob/master/DotnetCLIVersion.txt

[tmat]

OK, I'll use 2.1.503

[tmat]

Hmm, actually I'll do this as part of #2003. On it's own it might break repos that do not suppress nuget licenseurl warning.