Tests reporting BadImageFormatException

[bartelink]

master branch is failing with exeptions such as:

  ---- System.BadImageFormatException : An attempt was made to load a program with an incorrect format. (0x8007000B)
    at <StartupCode$FsCheck-Xunit-v3>.$PropertyAttribute.runner@217.InvokeTest(XunitTestRunnerContext ctxt, Object instance) in C:\Users\kurts\Projects\FsCheck\src\FsCheck.Xunit.v3\PropertyAttribute.fs:236
    ----- Inner Stack Trace -----
    at <StartupCode$FsCodec-Box>.$CoreCodec.Create@99-2.Invoke(Unit delegateArg0, FSharpValueOption`1 delegateArg1)
    at <StartupCode$FsCodec-Box>.$CoreCodec.Create@99-2.Invoke(Unit delegateArg0, FSharpValueOption`1 delegateArg1)
    at <StartupCode$FsCodec-Box>.$CoreCodec.down@74.Invoke(Context context, Event union) in /_//src/FsCodec.Box/CoreCodec.fs:75
    at <StartupCode$FsCodec-Box>.$CoreCodec.Create@77-1.Invoke(Context delegateArg0, Event delegateArg1)
    at <StartupCode$FsCodec-Box>.$CoreCodec.Create@39.FsCodec.IEventCodec<'Event, 'Body, 'Context>.Encode(Context context, Event event) in /_//src/FsCodec.Box/CoreCodec.fs:42
    at <StartupCode$FsCodec>.$FsCodec.MapBodies@162-4.FsCodec.IEventCodec<'Event, 'TargetFormat, 'Context>.Encode(Context context, Event event) in /_//src/FsCodec/FsCodec.fs:165
    at FsCodec.SystemTextJson.Tests.InteropTests.round-trips diverse bodies correctly(U x, Boolean encodeDirect, Boolean decodeDirect) in /_//tests/FsCodec.SystemTextJson.Tests/InteropTests.fs:42