Automatically build deb package on a new version tag

[MrSerth]

In #796, I noticed that the deb package was not build since an automation was missing.

With this PR, I add the missing automation.

I tested the workflow in my repo...

• when starting the workflow manually: https://github.com/MrSerth/pgcat/actions/runs/10737879151/job/29780286094
• when drafting a new release: https://github.com/MrSerth/pgcat/actions/runs/10737835796/job/29780146212

Obviously, both workflows failed since I cannot upload to the APT repo. However, the version substitution for the workflow is working correctly (as shown when collapsing the first line of the "Build and release package" step).

[drdrsh]

Thank you!