Add a protected modifier to the virtual property

Author: MaggieKimani1

src/Microsoft.OpenApi/Models/OpenApiHeader.cs

@@ -68,7 +68,7 @@ public class OpenApiHeader : IOpenApiSerializable, IOpenApiReferenceable, IOpenA
         /// <summary>
         /// The schema defining the type used for the header.
         /// </summary>
-        public virtual JsonSchema Schema { get; set; }
+        public virtual JsonSchema Schema { get; protected set; }
 
         /// <summary>
         /// Example of the media type.

src/Microsoft.OpenApi/Models/OpenApiMediaType.cs

@@ -20,7 +20,7 @@ public class OpenApiMediaType : IOpenApiSerializable, IOpenApiExtensible
         /// <summary>
         /// The schema defining the type used for the request body.
         /// </summary>
-        public virtual JsonSchema Schema { get; set; }
+        public virtual JsonSchema Schema { get; protected set; }
 
         /// <summary>
         /// Example of the media type.

src/Microsoft.OpenApi/Models/OpenApiParameter.cs

@@ -107,7 +107,7 @@ public virtual bool Explode
         /// <summary>
         /// The schema defining the type used for the request body.
         /// </summary>
-        public virtual JsonSchema Schema { get; set; }
+        public virtual JsonSchema Schema { get; protected set; }
 
         /// <summary>
         /// Examples of the media type. Each example SHOULD contain a value