ci: install zip for release packaging

The base package list only installed unzip; the packaging step uses
zip -qry for the release tarball, which failed with exit code 127.
The .deb was built successfully before the zip step aborted the job.

Author: hdp1972be-svg

.github/workflows/ubuntu-20.04-qt6-release.yml

@@ -52,7 +52,7 @@ jobs:
 
           apt-get update 2>&1 | tee logs/01-apt-update.log
           apt-get install -y --no-install-recommends \
-            bash ca-certificates git wget curl xz-utils file pkg-config unzip \
+            bash ca-certificates git wget curl xz-utils file pkg-config unzip zip \
             ninja-build build-essential python3 python3-pip sudo gdb \
             2>&1 | tee logs/02-base-packages.log