ci: promote preview .deb to stable on release (#10846)

The current CI job expects the release to have the `.deb` files
attached. Since writing that workflow, I've changed my mind on attaching
the `.deb` files there. Instead, they are only uploaded to the
repository. Without documentation on how to use them, these `.deb` files
are unlikely to provide a good user experience.

We change the job to instead promote the latest "preview` archives to
the stable repo.

scripts/sync-apt.sh

@@ -8,6 +8,7 @@
 # The `pool-` directories are referenced by the live repository metadata and the files in there need to atomically change with the metadata.
 
 set -euo pipefail
+shopt -s globstar
 
 COMPONENT="main"
 WORK_DIR="$(mktemp -d)"
@@ -57,7 +58,11 @@ for DISTRIBUTION in "stable" "preview"; do
     if [ "$(ls -A "${IMPORT_DIR}")" ]; then
         echo "Normalizing package names..."
 
-        for deb in "${IMPORT_DIR}"/*.deb; do
+        for deb in "${IMPORT_DIR}"/**; do
+            if [[ ! "$deb" == *.deb ]]; then
+                continue
+            fi
+
             if [ -f "$deb" ]; then
                 # Extract metadata from the .deb file
                 PACKAGE=$(dpkg-deb -f "$deb" Package 2>/dev/null)
@@ -85,7 +90,7 @@ for DISTRIBUTION in "stable" "preview"; do
         done
 
         echo "Importing new packages..."
-        mv --force --target-directory="${POOL_DIR}/" "${IMPORT_DIR}"/*.deb
+        mv --force --target-directory="${POOL_DIR}/" "${IMPORT_DIR}"/**/*.deb
     fi
 
     if [ -z "$(ls -A "${POOL_DIR}")" ]; then