investigate why sourcelink test fails for Windows action job

[shiftkey]

Example run: https://github.com/octokit/octokit.net/runs/411397758?check_suite_focus=true

Relevant output:

========================================
TestSourceLink
========================================
Executing task: TestSourceLink
Testing sourcelink info in packaging/Octokit.0.37.0-PullRequest2068-0019.nupkg
1 Documents without URLs:
bdbf6eb3afe9056e474d2ca2bec98a866c17b8a66405d1463fc9e8b8a832a65c sha256 csharp C:\Users\runneradmin\AppData\Local\Temp\.NETFramework,Version=v4.5.AssemblyAttributes.cs
1 Documents with errors:
417af2b5e83e7dc5e88dc35c32393712c9a2391596d6a366a44d9f13d898b369 sha256 csharp D:\a\octokit.net\octokit.net\Octokit\obj\Release\net45\Octokit.AssemblyInfo.cs
https://raw.githubusercontent.com/octokit/octokit.net/73e047c72d9ad8938366b6aa1386bdeba17899e0/Octokit/obj/Release/net45/Octokit.AssemblyInfo.cs
error: url failed NotFound: Not Found
sourcelink test failed
failed for lib/net45/Octokit.dll
 Documents without URLs:
50ddf2a6dd2a7d54b76e5119ea0685236fb6e703d82dc5a35d5d3683504f8f0d sha256 csharp C:\Users\runneradmin\AppData\Local\Temp\.NETFramework,Version=v4.6.AssemblyAttributes.cs
1 Documents with errors:
417af2b5e83e7dc5e88dc35c32393712c9a2391596d6a366a44d9f13d898b369 sha256 csharp D:\a\octokit.net\octokit.net\Octokit\obj\Release\net46\Octokit.AssemblyInfo.cs
https://raw.githubusercontent.com/octokit/octokit.net/73e047c72d9ad8938366b6aa1386bdeba17899e0/Octokit/obj/Release/net46/Octokit.AssemblyInfo.cs
error: url failed NotFound: Not Found
sourcelink test failed
failed for lib/net46/Octokit.dll
1 Documents without URLs:
e66dc6241c8fb7ec2a5a1179a4ba4587229ba0c0cf8328f52e061b610c675915 sha256 csharp C:\Users\runneradmin\AppData\Local\Temp\.NETStandard,Version=v1.1.AssemblyAttributes.cs
1 Documents with errors:
417af2b5e83e7dc5e88dc35c32393712c9a2391596d6a366a44d9f13d898b369 sha256 csharp D:\a\octokit.net\octokit.net\Octokit\obj\Release\netstandard1.1\Octokit.AssemblyInfo.cs
https://raw.githubusercontent.com/octokit/octokit.net/73e047c72d9ad8938366b6aa1386bdeba17899e0/Octokit/obj/Release/netstandard1.1/Octokit.AssemblyInfo.cs
error: url failed NotFound: Not Found
sourcelink test failed
failed for lib/netstandard1.1/Octokit.dll
1 Documents without URLs:
a6e03ae4df13fe05345e9022d1f1cd24ecae4bfd66db4843697c855d9f9335f4 sha256 csharp C:\Users\runneradmin\AppData\Local\Temp\.NETStandard,Version=v2.0.AssemblyAttributes.cs
1 Documents with errors:
417af2b5e83e7dc5e88dc35c32393712c9a2391596d6a366a44d9f13d898b369 sha256 csharp D:\a\octokit.net\octokit.net\Octokit\obj\Release\netstandard2.0\Octokit.AssemblyInfo.cs
 https://raw.githubusercontent.com/octokit/octokit.net/73e047c72d9ad8938366b6aa1386bdeba17899e0/Octokit/obj/Release/netstandard2.0/Octokit.AssemblyInfo.cs
error: url failed NotFound: Not Found
sourcelink test failed
failed for lib/netstandard2.0/Octokit.dll
4 files did not pass in D:/a/octokit.net/octokit.net/packaging/Octokit.0.37.0-PullRequest2068-0019.nupkg
An error occurred when executing task 'TestSourceLink'.
Error: Sourcelink test failed!
##[error]Process completed with exit code 1.

[shiftkey]

This isn't a Windows-specific issue, and I've isolated it to a combination of .NET Core 3.1 and Sourcelink not working together.

Repo: https://github.com/shiftkey/dotnetcore-sourcelink-test-bug/
Writeup and discussion: shiftkey/dotnetcore-sourcelink-test-bug#1

Closing this out for now because it's not worth also tracking here.