Require Microsoft.Bcl.AsyncInterfaces >=1.0.0 instead of =8.0.0

This technically fixes 2 different issues:
- previously SSH.NET would require exactly(!) version 8.0.0, which would
  cause issues in the future if e.g. a project using SSH.NET would
  try to update to version 9.0.0. In this case the constraint on the
  exact version would cause NuGet to refuse to upgrade to 9.0.0 (#1287)
- PowerShell Core seems to have problems with Version 8.0.0, therefore
  downgrade the requirement to 1.0.0 (see darkoperator/Posh-SSH#558)

build/nuget/SSH.NET.nuspec

@@ -17,10 +17,10 @@
         <tags>ssh scp sftp</tags>
         <dependencies>
           <group targetFramework="net462">
-            <dependency id="Microsoft.Bcl.AsyncInterfaces" version="[8.0.0]" />
+            <dependency id="Microsoft.Bcl.AsyncInterfaces" version="1.0.0" />
           </group>
           <group targetFramework="netstandard2.0">
-            <dependency id="Microsoft.Bcl.AsyncInterfaces" version="[8.0.0]" />
+            <dependency id="Microsoft.Bcl.AsyncInterfaces" version="1.0.0" />
             <dependency id="SshNet.Security.Cryptography" version="[1.3.0]" />
           </group>          
           <group targetFramework="netstandard2.1">

src/Renci.SshNet/Renci.SshNet.csproj

@@ -14,7 +14,7 @@
   </ItemGroup>
 
   <ItemGroup Condition=" '$(TargetFramework)' == 'net462' or '$(TargetFramework)' == 'netstandard2.0' ">
-    <PackageReference Include="Microsoft.Bcl.AsyncInterfaces" Version="8.0.0" />
+    <PackageReference Include="Microsoft.Bcl.AsyncInterfaces" Version="1.0.0" />
   </ItemGroup>
 
   <PropertyGroup Condition=" '$(TargetFramework)' == 'netstandard2.0' or '$(TargetFramework)' == 'netstandard2.1' or '$(TargetFramework)' == 'net6.0' or '$(TargetFramework)' == 'net7.0' or '$(TargetFramework)' == 'net8.0' ">