fix: mark methods as virtual for overriding

Author: MaggieKimani1

src/Microsoft.OpenApi/Models/OpenApiComponents.cs

@@ -98,7 +98,7 @@ public OpenApiComponents(OpenApiComponents? components)
         /// Serialize <see cref="OpenApiComponents"/> to Open API v3.1.
         /// </summary>
         /// <param name="writer"></param>
-        public void SerializeAsV31(IOpenApiWriter writer)
+        public virtual void SerializeAsV31(IOpenApiWriter writer)
         {
             Utils.CheckArgumentNull(writer);
 
@@ -136,7 +136,7 @@ public void SerializeAsV31(IOpenApiWriter writer)
         /// Serialize <see cref="OpenApiComponents"/> to v3.0
         /// </summary>
         /// <param name="writer"></param>
-        public void SerializeAsV3(IOpenApiWriter writer)
+        public virtual void SerializeAsV3(IOpenApiWriter writer)
         {
             Utils.CheckArgumentNull(writer);
 
@@ -338,7 +338,7 @@ private void RenderComponents(IOpenApiWriter writer, Action<IOpenApiWriter, IOpe
         /// <summary>
         /// Serialize <see cref="OpenApiComponents"/> to Open Api v2.0.
         /// </summary>
-        public void SerializeAsV2(IOpenApiWriter writer)
+        public virtual void SerializeAsV2(IOpenApiWriter writer)
         {
             // Components object does not exist in V2.
         }

src/Microsoft.OpenApi/Models/OpenApiSecurityRequirement.cs

@@ -35,7 +35,7 @@ public OpenApiSecurityRequirement()
         /// <summary>
         /// Serialize <see cref="OpenApiSecurityRequirement"/> to Open Api v3.1
         /// </summary>
-        public void SerializeAsV31(IOpenApiWriter writer)
+        public virtual void SerializeAsV31(IOpenApiWriter writer)
         {
             SerializeInternal(writer, (w, s) =>
             {
@@ -49,7 +49,7 @@ public void SerializeAsV31(IOpenApiWriter writer)
         /// <summary>
         /// Serialize <see cref="OpenApiSecurityRequirement"/> to Open Api v3.0
         /// </summary>
-        public void SerializeAsV3(IOpenApiWriter writer)
+        public virtual void SerializeAsV3(IOpenApiWriter writer)
         {
             SerializeInternal(writer, (w, s) =>
             {
@@ -96,7 +96,7 @@ private void SerializeInternal(IOpenApiWriter writer, Action<IOpenApiWriter, Ope
         /// <summary>
         /// Serialize <see cref="OpenApiSecurityRequirement"/> to Open Api v2.0
         /// </summary>
-        public void SerializeAsV2(IOpenApiWriter writer)
+        public virtual void SerializeAsV2(IOpenApiWriter writer)
         {
             SerializeInternal(writer, (w, s) => s.SerializeAsV2(w));
         }

src/Microsoft.OpenApi/Models/OpenApiTag.cs

@@ -46,7 +46,7 @@ internal OpenApiTag(IOpenApiTag tag)
         /// <summary>
         /// Serialize <see cref="OpenApiTag"/> to Open Api v3.1
         /// </summary>
-        public void SerializeAsV31(IOpenApiWriter writer) 
+        public virtual void SerializeAsV31(IOpenApiWriter writer) 
         {
             SerializeInternal(writer, OpenApiSpecVersion.OpenApi3_1,
                 (writer, element) => element.SerializeAsV31(writer));
@@ -55,7 +55,7 @@ public void SerializeAsV31(IOpenApiWriter writer)
         /// <summary>
         /// Serialize <see cref="OpenApiTag"/> to Open Api v3.0
         /// </summary>
-        public void SerializeAsV3(IOpenApiWriter writer) 
+        public virtual void SerializeAsV3(IOpenApiWriter writer) 
         {
             SerializeInternal(writer, OpenApiSpecVersion.OpenApi3_0,
                 (writer, element) => element.SerializeAsV3(writer));
@@ -84,7 +84,7 @@ internal void SerializeInternal(IOpenApiWriter writer, OpenApiSpecVersion versio
         /// <summary>
         /// Serialize <see cref="OpenApiTag"/> to Open Api v2.0
         /// </summary>
-        public void SerializeAsV2(IOpenApiWriter writer)
+        public virtual void SerializeAsV2(IOpenApiWriter writer)
         {
             writer.WriteStartObject();