fix: optimize repo sync command by using minimal-shallow variant and reducing parallel jobs

.github/actions/download-kernel/action.yml

@@ -62,8 +62,8 @@ runs:
 
         while [ $attempt -le $MAX_RETRIES ]; do
           echo "Attempt $attempt/$MAX_RETRIES: repo sync (timeout $SYNC_TIMEOUT)..."
-          #if timeout $SYNC_TIMEOUT repo sync -c -j16 --fail-fast --no-tags --force-sync --no-clone-bundle --optimized-fetch --retry-fetches=3; then
-          if timeout $SYNC_TIMEOUT repo sync -c --no-tags --no-clone-bundle --optimized-fetch --retry-fetches=3; then
+          # Use minimal-shallow variant: current-branch, shallow init done above, reduce files downloaded
+          if timeout $SYNC_TIMEOUT repo sync -c --current-branch --no-clone-bundle --no-tags --jobs-checkout=4 -j4; then
             echo "repo sync succeeded on attempt $attempt."
             break
           fi