Add MSVC 2026 to supported platforms


Configuration is in CI. Even though we do not ship dedicated packages
the compiler is supported.

Pick-to: 6.12
Change-Id: If939143f810f3dc8fcec7f01ac4cf3f033066f3c
Reviewed-by: Jani Heikkinen <jani.heikkinen@qt.io>
commit1599fe00c6dc13f2671727ab28a75a304b625186
parent8f15b1719da1b371189cc844b5069d4476c14d98
authorOliver Wolff <oliver.wolff@qt.io>
committerOliver Wolff <oliver.wolff@qt.io>
commit timeWed, 14 Oct 2026 07:42:42 +0000