ci: Migrate the Windows x64 job to Visual Studio 2026 on "windows-2025" The "windows-latest" alias was repointed to a Windows Server 2025 image that ships Visual Studio 2026 only, which prevented the version-exact generator "Visual Studio 17 2022" from matching any installed instance. This is a cherry-pick of commit dd5d363ae1fc7778f2734bf51b10d3fe65028671 from branch 'libpng18'.