ci: add 'self-hosted' tag to runs-on section

Fun fact: our self-hosted macOS runner has the same name as the one
provided by GitHub. Hence sometimes when no self-hosted runners are
available, the public GitHub one is chosen.

This patch enforces LuaJIT integration workflow to use only self-hosted
runner by explicitly specifying this in runs-on section.

NO_DOC=ci
NO_TEST=ci
NO_CHANGELOG=ci

Reviewed-by: Yaroslav Lobankov <y.lobankov@tarantool.org>
Signed-off-by: Igor Munkin <imun@tarantool.org>