Fix running tests on macOS 15

Author: atdrendel

Tests/AnyLanguageModelTests/APICompatibilityAnyLanguageModelTests.swift

@@ -3,8 +3,15 @@ import Testing
 #if canImport(FoundationModels)
     import AnyLanguageModel
 
+    private let isSystemLanguageModelAvailable: Bool = {
+        if #available(macOS 26.0, *) {
+            return SystemLanguageModel.default.isAvailable
+        }
+        return false
+    }()
+
     @available(macOS 26.0, *)
-    @Test("AnyLanguageModel Drop-In Compatibility", .enabled(if: SystemLanguageModel.default.isAvailable))
+    @Test("AnyLanguageModel Drop-In Compatibility", .enabled(if: isSystemLanguageModelAvailable))
     func anyLanguageModelCompatibility() async throws {
         let model = SystemLanguageModel.default
         let session = LanguageModelSession(

Tests/AnyLanguageModelTests/APICompatibilityFoundationModelsTests.swift

@@ -3,8 +3,18 @@ import Testing
 #if canImport(FoundationModels)
     import FoundationModels
 
+    private let isFoundationModelsSystemLanguageModelAvailable: Bool = {
+        if #available(macOS 26.0, *) {
+            return SystemLanguageModel.default.isAvailable
+        }
+        return false
+    }()
+
     @available(macOS 26.0, *)
-    @Test("FoundationModels Drop-In Compatibility", .enabled(if: SystemLanguageModel.default.isAvailable))
+    @Test(
+        "FoundationModels Drop-In Compatibility",
+        .enabled(if: isFoundationModelsSystemLanguageModelAvailable)
+    )
     func foundationModelsCompatibility() async throws {
         let model = SystemLanguageModel.default
         let session = LanguageModelSession(