Fix vinca-snapshot after change of get_released_repo signature

[traversaro]

I did not realized that the change in #87 was a breaking change, without this fix vinca-snapshot fails with:

traversaro@IITBMP014LW012:~/ros-jazzy$ pixi run vinca-snapshot
Package                                           Version
Traceback (most recent call last):
  File "/home/traversaro/ros-jazzy/.pixi/envs/default/bin/vinca-snapshot", line 10, in <module>
    sys.exit(main())
             ^^^^^^
  File "/home/traversaro/ros-jazzy/.pixi/envs/default/lib/python3.12/site-packages/vinca/snapshot.py", line 69, in main
    url, tag = distro.get_released_repo(dep)
    ^^^^^^^^
ValueError: too many values to unpack (expected 2)