Downgrade CommunityToolkit.Mvvm to v7.1.2 (#381)

Author: josesimoes

README-BEFORE-UPDATE-REFS.txt

@@ -5,4 +5,4 @@ IMPORTANT VERSION CONSTRAINTS:
   Reason: The VS2019 extension will fail due to a transitive dependency conflict between
           Compilers.Services.Unsafe and System.Collections.Immutable.
 - Can't update Polly beyond version 7.2.4 because of dependency conflicts with System.Threading.Tasks.Extensions.
-  
+- Can't update CommunityToolkit.Mvvm beyond v7.1.2 because of dependency conflicts with System.Threading.Tasks.Extensions in test framework.  

nanoFramework.Tools.DebugLibrary.Net/nanoFramework.Tools.DebugLibrary.Net.csproj

@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>library</OutputType>
     <TargetFrameworks>net6.0;net472</TargetFrameworks>
@@ -61,7 +61,7 @@
     <None Include="key.snk" />
   </ItemGroup>
   <ItemGroup>
-    <PackageReference Include="CommunityToolkit.Mvvm" Version="8.2.2" />
+    <PackageReference Include="CommunityToolkit.Mvvm" Version="7.1.2" />
     <PackageReference Include="Microsoft.SourceLink.GitHub">
       <Version>8.0.0</Version>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
@@ -83,4 +83,4 @@
     </PackageReference>
   </ItemGroup>
   <Import Project="..\nanoFramework.Tools.DebugLibrary.Shared\nanoFramework.Tools.DebugLibrary.Net.projitems" Label="Shared" />
-</Project>
+</Project>