Bump System.Text.Json from 4.7.2 to 8.0.3 in /csharp/src

Bumps [System.Text.Json](https://github.com/dotnet/runtime) from 4.7.2 to 8.0.3.
- [Release notes](https://github.com/dotnet/runtime/releases)
- [Commits](https://github.com/dotnet/runtime/commits/v8.0.3)

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

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

csharp/src/HMACSerialiser.csproj

@@ -32,7 +32,7 @@
  <ItemGroup>
  <PackageReference Include="System.Security.Cryptography.Algorithms" Version="4.3.1" />
  <PackageReference Include="System.Security.Cryptography.Primitives" Version="4.3.0" />
- <PackageReference Include="System.Text.Json" Version="4.7.2" />
+ <PackageReference Include="System.Text.Json" Version="8.0.3" />
  </ItemGroup>
 
 </Project>