feat: makes the reference interface covariant

Signed-off-by: Vincent Biret <[email protected]>

Author: baywet

src/Microsoft.OpenApi/Interfaces/IOpenApiReferenceableWithTarget.cs

@@ -7,7 +7,7 @@ namespace Microsoft.OpenApi.Interfaces
     /// A generic interface for OpenApiReferenceable objects that have a target.
     /// </summary>
     /// <typeparam name="T"></typeparam>
-    public interface IOpenApiReferenceableWithTarget<T> : IOpenApiReferenceable
+    public interface IOpenApiReferenceableWithTarget<out T> : IOpenApiReferenceable
     {
         /// <summary>
         /// Gets the resolved target object.

test/Microsoft.OpenApi.Tests/PublicApi/PublicApi.approved.txt

@@ -223,7 +223,7 @@ namespace Microsoft.OpenApi.Interfaces
         Microsoft.OpenApi.Models.OpenApiReference Reference { get; set; }
         bool UnresolvedReference { get; set; }
     }
-    public interface IOpenApiReferenceableWithTarget<T> : Microsoft.OpenApi.Interfaces.IOpenApiElement, Microsoft.OpenApi.Interfaces.IOpenApiReferenceable, Microsoft.OpenApi.Interfaces.IOpenApiSerializable
+    public interface IOpenApiReferenceableWithTarget<out T> : Microsoft.OpenApi.Interfaces.IOpenApiElement, Microsoft.OpenApi.Interfaces.IOpenApiReferenceable, Microsoft.OpenApi.Interfaces.IOpenApiSerializable
     {
         T Target { get; }
     }