test(schema): add deserialization tests for empty and boolean schemas

Add theory tests across OpenAPI 3.1 and 3.2 to validate deserialization of:
- Empty schema object ({})
- Boolean schema value (true)

These tests ensure that non-standard but valid schema forms are parsed
without errors and produce valid OpenApiSchema objects.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: baywet

test/Microsoft.OpenApi.Readers.Tests/V31Tests/OpenApiSchemaTests.cs

@@ -844,5 +844,17 @@ public void ParseSchemaWithoutUnevaluatedPropertiesDefaultsToTrue()
             Assert.Equivalent(expected, actual);
             Assert.True(actual.UnevaluatedProperties); // Explicitly verify the default
         }
+
+        [Theory]
+        [InlineData("{}")]
+        [InlineData("true")]
+        public void DeserializeBasicSchemaWorks(string schemaSource)
+        {
+            // Arrange & Act
+            var schema = OpenApiModelFactory.Parse<OpenApiSchema>(schemaSource, OpenApiSpecVersion.OpenApi3_1, new(), out _);
+
+            // Assert - schema should deserialize without error
+            Assert.NotNull(schema);
+        }
     }
 }

test/Microsoft.OpenApi.Readers.Tests/V32Tests/OpenApiSchemaTests.cs

@@ -695,6 +695,18 @@ public void ParseSchemaWithUnevaluatedPropertiesComplexSchema()
             // Assert
             Assert.Equivalent(expected, actual);
         }
+
+        [Theory]
+        [InlineData("{}")]
+        [InlineData("true")]
+        public void DeserializeBasicSchemaWorks(string schemaSource)
+        {
+            // Arrange & Act
+            var schema = OpenApiModelFactory.Parse<OpenApiSchema>(schemaSource, OpenApiSpecVersion.OpenApi3_2, new(), out _);
+
+            // Assert - schema should deserialize without error
+            Assert.NotNull(schema);
+        }
     }
 }