[Bug]: Need a way to represent null inside XML comments <example> tag.

### Describe the bug I can't find a way to return an example value of null for a string property. Our project does not have nullable reference types enabled, so by default a string variable/property is nullable. I've tried a couple of options: ``` public class Response { /// <example>null</example> public string Message{ get; set; } } ``` I've also tried: ``` public class Response { /// <example><see langword="null"/></example> public string Message{ get; set; } } ``` And: ``` public class Response { /// <example xsi:nil="true"/> public string Message{ get; set; } } ``` but none of these end up in getting a null value into the example swagger documentation. The generated documentation shows the example as: `"message": "null",` ### Expected behavior I would like this xml example comment ``` /// <example>null</example> public string Message{ get; set; } ``` to generate an example like this: `"message": null` ### Actual behavior generates as if null is a literal string value: `"message": "null",` ### Steps to reproduce _No response_ ### Exception(s) (if any) _No response_ ### Swashbuckle.AspNetCore version 10.1.0 ### .NET Version <TargetFramework>net10.0</TargetFramework> ### Anything else? Seems to be a regression of this issue that was resolved a long time ago: https://github.com/domaindrivendev/Swashbuckle.AspNetCore/issues/1768 And seems to have regressed here: https://github.com/domaindrivendev/Swashbuckle.AspNetCore/pull/3283 I can see there was a unit test for the earlier issue that was changed in a way to make the test pass, but the result is not correct/desired. The change to the unit test is here: test/Swashbuckle.AspNetCore.SwaggerGen.Test/XmlComments/XmlCommentsSchemaFilterTests.cs Changed from `{ typeof(XmlAnnotatedType), nameof(XmlAnnotatedType.StringPropertyWithNullExample), JsonSchemaTypes.String, "null" },` to `{ typeof(XmlAnnotatedType), nameof(XmlAnnotatedType.StringPropertyWithNullExample), JsonSchemaTypes.String, "\"null\"" },` But that changes the whole purpose of the test, which is to be able to generate an example with a null string value. Not a literal "null".