Switch to the new Mono.Unix nuget

The nuget replaces older `Mono.Posix-NETStandard` one and makes it
possible to build LibZipSharp using `dotnet` on Unix.

Author: grendello

LibZipSharp.UnitTest/LibZipSharp.UnitTest.csproj

@@ -18,7 +18,7 @@
  <PackageReferenceInclude="Microsoft.NET.Test.Sdk"Version="16.8.3" />
  <PackageReferenceInclude="Xamarin.LibZipSharp"Version="$(_LibZipSharpNugetVersion)"Condition="'$(ReferenceNuget)' == 'True'" />
  <PackageReferenceInclude="NUnit.ConsoleRunner"Version="3.11.1" />
- <PackageReferenceInclude="Mono.Posix.NETStandard"Version="1.0.0" />
+ <PackageReferenceInclude="Mono.Unix"Version="$(_MonoPosixNugetVersion)" />
  </ItemGroup>
 
  <ItemGroup>

LibZipSharp.props

@@ -3,6 +3,7 @@
  <_LibZipSharpNugetVersion>2.0.0</_LibZipSharpNugetVersion>
  <_NativeBuildDir>$(MSBuildThisFileDirectory)lzsbuild</_NativeBuildDir>
  <_ExternalDir>$(MSBuildThisFileDirectory)external</_ExternalDir>
+ <_MonoPosixNugetVersion>7.0.0-alpha.21276.2</_MonoPosixNugetVersion>
  <UseXZCondition=" '$(UseXZ)' == '' ">false</UseXZ>
  </PropertyGroup>
 </Project>