fix: freeze System.Text.Json versions for older frameworks

Author: vbreuss

Directory.Packages.props

@@ -3,10 +3,10 @@
     <ManagePackageVersionsCentrally>true</ManagePackageVersionsCentrally>
   </PropertyGroup>
     <ItemGroup Condition=" '$(TargetFramework)' == 'net6.0' ">
-        <PackageVersion Include="System.Text.Json" Version="10.0.2"/>
+        <PackageVersion Include="System.Text.Json" Version="[6.0.11]"/>
     </ItemGroup>
     <ItemGroup Condition=" '$(TargetFramework)' == 'net8.0' ">
-        <PackageVersion Include="System.Text.Json" Version="10.0.2"/>
+        <PackageVersion Include="System.Text.Json" Version="[8.0.6]"/>
     </ItemGroup>
     <ItemGroup Condition=" '$(TargetFramework)' != 'net8.0' And '$(TargetFramework)' != 'net6.0' ">
         <PackageVersion Include="System.Text.Json" Version="10.0.2"/>