ci: fix deb build

It seems that something has been changed in the package dependencies
and `install` no longer works here without `update`.

Author: DifferentialOrange

Diff for: .github/workflows/packing.yml

@@ -414,6 +414,7 @@ jobs:
 
       - name: Install deb packing tools
         run: |
+          sudo apt update
           sudo apt install -y devscripts equivs
 
       - name: Make changelog entry for non-release build