Fix default runner alpine flavour version
The alpine runner flavour should default to 3.19, not 3.18.
See: https://gitlab.com/gitlab-org/gitlab-runner/-/issues/37654#note_1969160620
The alpine runner flavour should default to 3.19, not 3.18.
See: https://gitlab.com/gitlab-org/gitlab-runner/-/issues/37654#note_1969160620