CI: re-enable the beaker_in_container acceptance job to cover in-container connection routing

[miharp]

Background

.github/workflows/test.yml contains a commented-out beaker_in_container acceptance job that ran Beaker itself inside a container (with DOCKER_IN_DOCKER=true) and then provisioned test containers from there. It was disabled with the note:

this job is currently broken because puppet/puppet-dev-tools:2023-02-24-1bca42e is too old

Why it matters

Some code paths in the hypervisor only trigger when Beaker runs inside a container, and none of the current CI jobs exercise them:

• in_container? — used to decide whether to connect to test containers via the container network gateway/IP instead of a published host port. Fix ssh connection routing under Podman: network naming and container detection #194 extends this check to detect Podman containers (/run/.containerenv in addition to /.dockerenv), but CI can't currently validate either variant.
• The gateway-based connection routing in get_ssh_connection_info (the DOCKER_IN_DOCKER / in_container? branch).

Suggested work

• Revive the beaker_in_container job with a maintained image (or just a plain Ruby image with bundle install, as the old step already did).
• Ideally add a Podman variant (Beaker running inside a Podman container against the Podman socket) so the /run/.containerenv detection path from Fix ssh connection routing under Podman: network naming and container detection #194 is covered too.

Follow-up from the review discussion on #194.

[miharp]

Scope note: the fix will cover both in-container routing modes, each under Docker and rootless Podman (4-job matrix): auto-detected containment (gateway + published ssh port; the path #194 touches) and explicit DOCKER_IN_DOCKER=true (direct container IP; what the original job tested). These are separate branches in get_ssh_connection_info, not one path as the issue text implies. The container image version will be derived from the gemspec's required_ruby_version, so there is no separately maintained version string. PR to follow once #194 lands.