CI: Use windows-2025-vs2026 in the GMT Dev Tests workflow

Xref https://github.blog/changelog/2026-05-14-github-actions-upcoming-image-migrations/#windows-2025-visual-studio-2026-image-migration

Author: weiji14

.github/workflows/ci_tests_dev.yaml

@@ -39,7 +39,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-24.04, ubuntu-24.04-arm, macos-26, windows-2025]
+        os: [ubuntu-24.04, ubuntu-24.04-arm, macos-26, windows-2025-vs2026]
         gmt_git_ref: [master]
     timeout-minutes: 30
     defaults: