build: bump System.Text.Json

Bumps [System.Text.Json](https://github.com/dotnet/runtime) from 8.0.4 to 9.0.0.
- [Release notes](https://github.com/dotnet/runtime/releases)
- [Commits](dotnet/runtime@v8.0.4...v9.0.0)

---
updated-dependencies:
- dependency-name: System.Text.Json
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

App/kernel-memory/Directory.Packages.props

@@ -53,7 +53,7 @@
     <PackageVersion Include="System.Linq.Async" Version="6.0.1" />
     <PackageVersion Include="System.Memory.Data" Version="8.0.0" />
     <PackageVersion Include="System.Numerics.Tensors" Version="9.0.0" />
-    <PackageVersion Include="System.Text.Json" Version="8.0.4" />
+    <PackageVersion Include="System.Text.Json" Version="9.0.0" />
     <PackageVersion Include="Tiktoken" Version="2.0.3" />
   </ItemGroup>
   <!-- OpenXml blocked, do not upgrade these -->