fix: correct deserialization and test for UnevaluatedPropertiesSchema

- Fix deserialization to use ValueNode check like AdditionalProperties
- Fix copy constructor test to properly cast before modifying
- Update PublicAPI.Unshipped.txt with new API surface
- Update global.json to use available SDK version
- All UnevaluatedProperties tests now passing

Co-authored-by: baywet <7905502+baywet@users.noreply.github.com>

Author: Copilot

global.json

@@ -1,5 +1,5 @@
 {
   "sdk": {
-    "version": "8.0.415"
+    "version": "8.0.417"
   }
 }

src/Microsoft.OpenApi/PublicAPI.Unshipped.txt

@@ -1 +1,6 @@
 #nullable enable
+Microsoft.OpenApi.IOpenApiSchemaWithUnevaluatedProperties
+Microsoft.OpenApi.IOpenApiSchemaWithUnevaluatedProperties.UnevaluatedPropertiesSchema.get -> Microsoft.OpenApi.IOpenApiSchema?
+Microsoft.OpenApi.OpenApiSchema.UnevaluatedPropertiesSchema.get -> Microsoft.OpenApi.IOpenApiSchema?
+Microsoft.OpenApi.OpenApiSchema.UnevaluatedPropertiesSchema.set -> void
+Microsoft.OpenApi.OpenApiSchemaReference.UnevaluatedPropertiesSchema.get -> Microsoft.OpenApi.IOpenApiSchema?

src/Microsoft.OpenApi/Reader/V31/OpenApiSchemaDeserializer.cs

@@ -149,13 +149,12 @@ internal static partial class OpenApiV31Deserializer
             (o, n, t) =>
             {
                 // Handle both boolean (false/true) and schema object cases
-                var scalarValue = n.GetScalarValue();
-                if (scalarValue != null)
+                if (n is ValueNode)
                 {
-                    // Boolean case: false means no unevaluated properties, true is default (ignore)
-                    if (bool.TryParse(scalarValue, out var boolValue))
+                    var value = n.GetScalarValue();
+                    if (value is not null)
                     {
-                        o.UnevaluatedProperties = boolValue;
+                        o.UnevaluatedProperties = bool.Parse(value);
                     }
                 }
                 else

test/Microsoft.OpenApi.Tests/Models/OpenApiSchemaTests.cs

@@ -514,7 +514,8 @@ public void OpenApiSchemaCopyConstructorWithUnevaluatedPropertiesSchemaSucceeds(
             Assert.NotSame(baseSchema.UnevaluatedPropertiesSchema, actualSchema.UnevaluatedPropertiesSchema);
 
             // Verify that changing the copy doesn't affect the original
-            actualSchema.UnevaluatedPropertiesSchema.MaxLength = 200;
+            var actualSchemaTyped = Assert.IsType<OpenApiSchema>(actualSchema.UnevaluatedPropertiesSchema);
+            actualSchemaTyped.MaxLength = 200;
             Assert.Equal(100, baseSchema.UnevaluatedPropertiesSchema.MaxLength);
         }