"Could not find part of path to System.Runtime.CompilerServices.Unsafe.dll" when installing nuget packages

I'm attempting to install some nuget packages into my project and keep getting an error that looks like this:

Could not find a part of the path 'C:\<path to my project>\packages\System.Runtime.CompilerServices.Unsafe.6.0.0\lib\net461\System.Runtime.CompilerServices.Unsafe.dll'

I have tried installing the nuget package for System.Runtime.CompilerServices.Unsafe but that gave me the same issue.

I also tried downloading System.Runtime.CompilerServices.Unsafe directly from the nuget website and using gacutil on it but that did not change anything.