docker: fix umount when busy

before:
+ fusermount3 -u /encrypted
fusermount3: failed to unmount /encrypted: Resource busy

docker/rgpgfs_unattended.sh

@@ -38,7 +38,7 @@ set -x
 grep -q "^trust-model always$" ~/.gnupg/gpg.conf 2> /dev/null \
     || echo trust-model always | tee ~/.gnupg/gpg.conf
 
-trap 'fusermount3 -u "$CIPHER_DIR"' SIGTERM
+trap 'fusermount3 -u -z "$CIPHER_DIR"' SIGTERM
 rgpgfs -f -o allow_other \
     -o modules=subdir,subdir="$SOURCE_DIR" \
     -o recipient="$RECIPIENT" \