CI update.
* ps/ci-gitlab-msvc-updates:
gitlab-ci: handle failed tests on MSVC+Meson job
gitlab-ci: use "run-test-slice-meson.sh"
ci: make test slicing consistent across Meson/Make
github: fix Meson tests not executing at all
meson: fix MERGE_TOOL_DIR with "--no-bin-wrappers"
ci: don't skip smallest test slice in GitLab
ci: handle failures of test-slice helper