Missing System.Runtime core assembly

[olafurpg]

Steps to reproduce

• Clone repo belav/csharpier
• Run scip-dotnet index
• Run scip snapshot. See the following errors

Src/CSharpier.Cli/StdOutFormattedFileWriter.cs: use --strict=false to ignore this error: scip-dotnet nuget <Missing Core Assembly> 0.0.0.0 System/Object#: empty identifier
scip-dotnet nuget <Missing Core Assembly> 0.0.0.0 System/Object#
_________________________________________^

These symbols belong to the System.Runtime package, which we're able to resolve in our snapshot tests.

https://github.com/sourcegraph/scip-dotnet/blob/main/snapshots/output/syntax/Main/Methods.cs#L10