GitHub CI: update tested macOS 14 -> 15 and Windows Server 2022 -> 2025

Author: greenrobot-team

.github/workflows/test.yml

@@ -59,8 +59,8 @@ jobs:
       fail-fast: false # To see all Dart SDKs that fail, also sometimes with more helpful errors.
       matrix:
         os:
-          - windows-2022
-          - macos-14
+          - windows-2025
+          - macos-15
           - ubuntu-24.04
         sdk:
           # Test latest available and lowest supported SDK (see dev-doc/updating-dart-flutter-and-dependencies.md).
@@ -103,9 +103,9 @@ jobs:
       fail-fast: false
       matrix:
         os:
-          - macos-14
+          - macos-15
           - ubuntu-24.04
-          - windows-2022 # Flutter 2.9 and newer need Visual Studio 2022 to build for desktop
+          - windows-2025
         flutter-version:
           # Test latest available and lowest supported SDK (see dev-doc/updating-dart-flutter-and-dependencies.md).
           # Pick a concrete version instead of "latest" to avoid builds breaking due to changes in new SDKs.