Update to preview 7

Author: bkoelman

test/JsonApiDotNetCoreTests/JsonApiDotNetCoreTests.csproj

@@ -21,6 +21,6 @@
     <PackageReference Include="Microsoft.EntityFrameworkCore.InMemory" Version="$(EFCoreVersion)" />
     <PackageReference Include="Microsoft.EntityFrameworkCore.Proxies" Version="$(EFCoreVersion)" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="$(TestSdkVersion)" />
-    <PackageReference Include="System.Text.Json" Version="7.0.0-preview.5.22301.12" />
+    <PackageReference Include="System.Text.Json" Version="7.0.0-preview.7.22375.6" />
   </ItemGroup>
 </Project>