Add tests for version flag

.gitlab-ci.yml

buffyboard/test/build.sh

buffyboard/test/helpers.sh

buffyboard/test/test-all.sh

buffyboard/test/test-version-matches-meson-and-changelog.sh

test/helpers.sh

unl0kr/test/helpers.sh

...-uses-drm-backend-if-selected-via-config-and-available.sh

unl0kr/test/test-uses-fb-backend-by-default.sh

...-fb-backend-if-drm-selected-via-config-but-unavailable.sh

unl0kr/test/test-uses-fb-backend-if-selected-via-config.sh

unl0kr/test/test-version-matches-meson-and-changelog.sh

unl0kr/test/test-with-drm.sh

unl0kr/test/test-without-drm.sh