Bump System.Text.Json from 8.0.5 to 9.0.0 in /src

Bumps [System.Text.Json](https://github.com/dotnet/runtime) from 8.0.5 to 9.0.0.
- [Release notes](https://github.com/dotnet/runtime/releases)
- [Commits](dotnet/runtime@v8.0.5...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]>

src/Fdc3.Json/Finos.Fdc3.Json.csproj

@@ -35,7 +35,7 @@
     </ItemGroup>
 
     <ItemGroup>
-        <PackageReference Include="System.Text.Json" Version="8.0.5" />
+        <PackageReference Include="System.Text.Json" Version="9.0.0" />
     </ItemGroup>
 
     <ItemGroup>