Update dependency DocumentFormat.OpenXml to v2.20.0 · DFE-Digital/prepare-academy-conversions@996f610

Process completed with exit code 1.

Possible null reference argument for parameter 'uri' in 'UriBuilder.UriBuilder(string uri)'.

Possible null reference argument for parameter 's' in 'int int.Parse(string s, NumberStyles style)'.

ModelState.IsValid should be checked in controller actions. (https://rules.sonarsource.com/csharp/RSPEC-6967)