wip/texturesharing-5.12 branch is CI-tested against dev branch

All integrations fail for the newly created qtwayland/wip/texturesharing-5.12 branch, since it tries to build against the dev branch of qtbase and qtdeclarative.

There are two possible solutions: either build against 5.12, or disable CI. The purpose of this branch is to publish a backport of a specific feature, so the changes will never end up in a Qt release. CI would of course be useful to guard against errors in conflict resolution, but this is not critical.