[Fix] Workflows: Disable publishing when building the AppImage

[CommandMC]

Electron-Builder tries to be smart and auto-enables publishing if if's on the main branch of a repo (at least it seems that way, it doesn't do this in the PR workflow; can't find anything about this in the docs), which then promptly fails.
Explicitly turn it off

I can't test this locally, let's hope 3rd time's the charm

---

Use the following Checklist if you have changed something on the Backend or Frontend:

• Tested the feature and it's working on a current and clean install.
• Tested the main App features and they are still working on a current and clean install. (Login, Install, Play, Uninstall, Move games, etc.)
• Created / Updated Tests (If necessary)
• Created / Updated documentation (If necessary)

[flavioislima]

should work now