✅enable to run unit tests in .NET 472

[fforjan]

This enables to run unit test in .Net 472.

It also fixes one issue when using .Net472 - we found it when following the steps from the Readme.MD

[fforjan]

Notice that build on linux only run for net80

While for windows, you would see:

Failed!  - Failed:    29, Passed:   160, Skipped:     2, Total:   191, Duration: 734 ms - Wasmtime.Tests.dll (net472)
Failed!  - Failed:    19, Passed:    80, Skipped:     0, Total:    99, Duration: 278 ms - Wasmtime.Tests.dll (net8.0)

[jsturtevant]

@fforjan could you rebase this PR? I will take a closer look afterwards

[fforjan]

@jsturtevant should be good now

[fforjan]

@jsturtevant let me know if you would like me to do anything