Bump System.Text.Json in /aspnet-samples/AdvancedChatRoom (#289)

Bumps [System.Text.Json](https://github.com/dotnet/runtime) from 8.0.3 to 8.0.4.
- [Release notes](https://github.com/dotnet/runtime/releases)
- [Commits](dotnet/runtime@v8.0.3...v8.0.4)

---
updated-dependencies:
- dependency-name: System.Text.Json
  dependency-type: direct:production
...

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aspnet-samples/AdvancedChatRoom/AdvancedChatRoom.csproj

@@ -315,8 +315,9 @@
     <Reference Include="System.Text.Encodings.Web, Version=8.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51, processorArchitecture=MSIL">
       <HintPath>..\packages\System.Text.Encodings.Web.8.0.0\lib\net462\System.Text.Encodings.Web.dll</HintPath>
     </Reference>
-    <Reference Include="System.Text.Json, Version=8.0.0.3, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51, processorArchitecture=MSIL">
-      <HintPath>..\packages\System.Text.Json.8.0.3\lib\net462\System.Text.Json.dll</HintPath>
+    <Reference Include="System.Text.Json, Version=8.0.0.4, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51">
+      <HintPath>..\packages\System.Text.Json.8.0.4\lib\net462\System.Text.Json.dll</HintPath>
+      <Private>True</Private>
     </Reference>
     <Reference Include="System.Threading.Channels, Version=4.0.1.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51, processorArchitecture=MSIL">
       <HintPath>..\packages\System.Threading.Channels.4.6.0\lib\netstandard2.0\System.Threading.Channels.dll</HintPath>