Bump version to 6.12.0


Change-Id: Iba3af2ad72cb4de0806917efcfb56c85bb5a6ef0
Reviewed-by: Akseli Salovaara <akseli.salovaara@qt.io>
commit17a7f904558b554baaf3dc51d8f26d4de7459845
parente6b9e1e457aa66aaa4884868096bb4dcfc7bf5b0
authorJani Heikkinen <jani.heikkinen@qt.io>
committerJani Heikkinen <jani.heikkinen@qt.io>
commit timeTue, 16 Dec 2025 22:38:17 +0000