Add a test for syncing an image with PQC manifest signatures

[dralley]

📜 Checklist

• Commits are cleanly separated with meaningful messages (simple features and bug fixes should be squashed to one commit)
• A changelog entry or entries has been added for any significant changes
• Follows the Pulp policy on AI Usage
• (For new features) - User documentation and test coverage has been added

See: Pull Request Walkthrough

[dralley]

Previous (expected) failure without xfail: https://github.com/pulp/pulp_container/actions/runs/23649497083/job/68890463487#step:14:4399

[patchback]

Backport to 2.19: 💚 backport PR created

✅ Backport PR branch: patchback/backports/2.19/b31981db27701132642759466ed0866c3aa999bc/pr-2279

Backported as #2283

🤖 @patchback
I'm built with octomachinery and
my source is open — https://github.com/sanitizers/patchback-github-app.

[patchback]

Backport to 2.26: 💚 backport PR created

✅ Backport PR branch: patchback/backports/2.26/b31981db27701132642759466ed0866c3aa999bc/pr-2279

Backported as #2282

🤖 @patchback
I'm built with octomachinery and
my source is open — https://github.com/sanitizers/patchback-github-app.

[patchback]

Backport to 2.24: 💚 backport PR created

✅ Backport PR branch: patchback/backports/2.24/b31981db27701132642759466ed0866c3aa999bc/pr-2279

Backported as #2284

🤖 @patchback
I'm built with octomachinery and
my source is open — https://github.com/sanitizers/patchback-github-app.

[patchback]

Backport to 2.27: 💚 backport PR created

✅ Backport PR branch: patchback/backports/2.27/b31981db27701132642759466ed0866c3aa999bc/pr-2279

Backported as #2285

🤖 @patchback
I'm built with octomachinery and
my source is open — https://github.com/sanitizers/patchback-github-app.

[patchback]

Backport to 2.20: 💚 backport PR created

✅ Backport PR branch: patchback/backports/2.20/b31981db27701132642759466ed0866c3aa999bc/pr-2279

Backported as #2287

🤖 @patchback
I'm built with octomachinery and
my source is open — https://github.com/sanitizers/patchback-github-app.

[patchback]

Backport to 2.22: 💚 backport PR created

✅ Backport PR branch: patchback/backports/2.22/b31981db27701132642759466ed0866c3aa999bc/pr-2279

Backported as #2286

🤖 @patchback
I'm built with octomachinery and
my source is open — https://github.com/sanitizers/patchback-github-app.