fix(test): use fixed podman:v5.7 version and fix test image startup issue

[reubenmiller]

Fix an issue with the podman >= 5.6 container images, where the systemd-firstboot service would hang causing other services to fail to start.

To keep the system test images stage, a fixed version v5.7 is now used in the podman v5 line to avoid the systems tests breaking unexpectedly over time which blocks new thin-edge.io releases.

[github-actions]

Robot Results

✅ Passed	❌ Failed	⏭️ Skipped	Total	Pass %	⏱️ Duration
21	0	1	21	100	9m3.838749s

Passed Tests

Name	⏱️ Duration	Suite
Supports Cumulocity Basic Auth Credentials	20.134 s	C8Y-Basic-Auth
Ignore Containers Marked With A Specific Label	29.345 s	Container
Grace period to allow container to startup	5.026 s	Operations
Service is up	0.193 s	Operations
Get Logfile Request	4.810 s	Operations
Get Configuration File	5.267 s	Operations
Set Configuration File	2.878 s	Operations
Execute Shell Command	2.649 s	Operations
Install application using docker compose	24.831 s	Operations
Get Container Logs	4.820 s	Operations
Get Container Logs without explicit container name	4.827 s	Operations
Get Container Logs For Non-existent container	2.651 s	Operations
Update From Legacy Versions	141.381 s	Self-Update-Compat
Trigger self update via local command	27.181 s	Self-Update
Self update should only update if there is a new image	22.036 s	Self-Update
Self update using software update operation	103.487 s	Self-Update
Rollback when trying to install a non-tedge based image	24.613 s	Self-Update
Self update using software update operation using Container type	116.039 s	Self-Update
Cloud Connection is Online	0.298 s	Telemetry
Service status	0.378 s	Telemetry
Sends measurements	0.972 s	Telemetry