Update to coin_module_test_template_v3.yaml

- The main differences between v2 and v3 are:
  * `coin_module_test_template_v2.yaml` ignores autotest return
    codes because the `COIN_CTEST_IGNORE_EXIT_CODE` flag is set.
  * The Axivion build was moved from coin_module_build_template_v2.yaml
    to coin_module_test_template_v3.yaml in commit
    c3ddec2f15a1cf806d8df444952cb2c2231ae4ad
- Switch the qtmqtt submodule to the newer v3 version to improve
the submodule CI experience for autotests and restore Axivion
checks.

Pick-to: 6.12 6.11
Change-Id: I1695c8ca1af616512dff437a0a4cdbd0491412d4
Reviewed-by: Toni Saario <toni.saario@qt.io>