Extend CI coverage for meta-qt6

The bitbake override syntax support was backported to older yocto release (hardknott, gatesgarth and dunfell). The CI coverate for meta-qt6 should be extend to cover more yocto versions now that it possible.

For 6.2, to more recent version should be added. Target is at least to have the next LTS (kirkstone) tested.

6.3/dev: at least the previous LTS release (dunfell) should be tested.