Missing APT pinning for Icedove
Apparently nothing prevents us from installing Icedove from Debian, without our patches, except our hopefully higher version number. But it happens that we’re lagging behind (#11530 (closed)), so we need to add APT pinning to prevent that.
Feature Branch: feature/11714-icedove-45.2.0-1
Parent Task: #5663 (closed)
Original created by @intrigeri on 11613 (Redmine)