Pass tags as list for consistency with Java implementation (confluentinc#2343)

Author: rayokota

src/Confluent.SchemaRegistry.Rules/CelFieldExecutor.cs

@@ -65,7 +65,7 @@ public async Task<object> Transform(RuleContext ctx, RuleContext.FieldContext fi
                         { "fullName", fieldCtx.FullName },
                         { "name", fieldCtx.Name },
                         { "typeName", fieldCtx.Type.ToString().ToUpper() },
-                        { "tags", fieldCtx.Tags },
+                        { "tags", fieldCtx.Tags.ToList() },
                         { "message", message }
                     }
                 );