Update Todoist.Net project and package versions

The Todoist.Net version has been updated from 7.0.0 to 8.0.0. Additionally, the System.Text.Json package version has been incremented from 8.0.3 to 8.0.4, and the xunit version in the Todoist.Net.Tests project has been upgraded from 2.8.1 to 2.9.0.

Author: olsh

src/Todoist.Net.Tests/Todoist.Net.Tests.csproj

@@ -7,7 +7,7 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.10.0" />
-    <PackageReference Include="xunit" Version="2.8.1" />
+    <PackageReference Include="xunit" Version="2.9.0" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.8.1">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>

src/Todoist.Net/Todoist.Net.csproj

@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <Description>A Todoist API client for .NET</Description>
-    <VersionPrefix>7.0.0</VersionPrefix>
+    <VersionPrefix>8.0.0</VersionPrefix>
     <Authors>Oleg Shevchenko, Ahmed Zaki</Authors>
     <TargetFrameworks>netstandard2.0;net462</TargetFrameworks>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
@@ -26,7 +26,7 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.CSharp" Version="4.7.0" />
     <PackageReference Include="Microsoft.SourceLink.GitHub" Version="8.0.0" PrivateAssets="All" />
-    <PackageReference Include="System.Text.Json" Version="8.0.3" />
+    <PackageReference Include="System.Text.Json" Version="8.0.4" />
   </ItemGroup>
 
   <ItemGroup Condition=" '$(TargetFramework)' == 'net462' ">