Minor tweaks

[AlekSi]

No description provided.

PR Overview

This PR introduces minor tweaks to the packaging commands and testing outputs.

• Introduces a new command-line flag "debian-only" in main.go to limit output to Debian package versions.
• Updates the GitHub workflow and test expectations to reflect the new flag and table header format.
• Adjusts the output formatting in docker.go and docker_test.go to use "Docker image" consistently.

Reviewed Changes

File	Description
ferretdb_packaging/defineversion/main.go	Added the "-debian-only" flag and updated conditional output logic.
.github/workflows/ferretdb_packages.yml	Modified run commands to include the "-debian-only" flag and updated artifact names.
ferretdb_packaging/defineversion/docker_test.go	Updated expected outputs in tests to match new image tags and table header formatting.
ferretdb_packaging/defineversion/docker.go	Changed table header labels in dockerSummary for consistency with tests.

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.