Fix package validation errors

[khvn26]

The following errors are seen when validating a locally built package:

{
  "Packages": {
    "/Users/kgustyr/dev/flagsmith/flagsmith-dotnet-client/Flagsmith.FlagsmithClient/bin/Release/Flagsmith.5.3.0.nupkg": {
      "Errors": [
        {
          "ErrorCode": 101,
          "Message": "XML documentation not found",
          "HelpText": "lib/netstandard2.0/Flagsmith.Engine.dll"
        },
        {
          "ErrorCode": 101,
          "Message": "XML documentation not found",
          "HelpText": "lib/netstandard2.0/Flagsmith.FlagsmithClient.dll"
        },
        {
          "ErrorCode": 111,
          "Message": "Symbol file not found",
          "FileName": "lib/netstandard2.0/Flagsmith.FlagsmithClient.dll"
        },
        {
          "ErrorCode": 111,
          "Message": "Symbol file not found",
          "FileName": "lib/netstandard2.0/Flagsmith.Engine.dll"
        },
        {
          "ErrorCode": 74,
          "Message": "Repository commit is not set"
        },
        {
          "ErrorCode": 72,
          "Message": "Repository type is not set"
        },
        {
          "ErrorCode": 61,
          "Message": "Readme is not set"
        },
        {
          "ErrorCode": 12,
          "Message": "\u003Cauthors\u003E element is not set explicitly (same as \u003Cid\u003E)"
        }
      ]
    }
  }
}

These need to be resolved and removed from the --excluded-rule-ids validator argument in the release workflow.