Fix package validation errors

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

```json
{
"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.