chore(linux): Disable Mantic builds on Launchpad

Mantic builds currently fail because there's a newer ibus version in
the official Ubuntu repos that overrides our patched ibus version.
Ubuntu is trying to get ibus 1.5.29-beta to work so there are often
new packages. We wait until that stabilized before we're providing a
new patched ibus version at which point we can enable building for
Ubuntu 23.10 Mantic.

Closes #9428.