[Github] Use zstd to compress CI container images

zstd usually offers better compression ratios, but also offers much
higher decompression speeds, which can tangibly impact image unpack
times. Enable this by default given it is a two line change that is
transparent at image pull time given most container runtimes these days
supported zstd compressed images.

Author: boomanaiden154

.github/actions/push-container/action.yml

@@ -24,9 +24,9 @@ runs:
           latest_name=$(echo $image_name | sed 's/:[a-f0-9]\+$/:latest/g')
           podman tag $image_name $latest_name
           echo "Pushing $image_name ..."
-          podman push $image_name
+          podman push --compression-format=zstd $image_name
           echo "Pushing $latest_name ..."
-          podman push $latest_name
+          podman push --compression-format=zstd $latest_name
         }
 
         podman login -u ${{ github.actor }} -p $GITHUB_TOKEN ghcr.io