Fix possible update failure on xenial

helpers.sh

@@ -234,6 +234,9 @@ docker_update() {
             "deb [arch="$(dpkg --print-architecture)" signed-by=/etc/apt/keyrings/docker.gpg] https://download.docker.com/linux/ubuntu \
             bionic stable" | \
             tee /etc/apt/sources.list.d/docker.list > /dev/null
+            mkdir -p /etc/apt/keyrings
+            rm -f /etc/apt/keyrings/docker.gpg
+            curl -fsSL https://download.docker.com/linux/ubuntu/gpg | gpg --dearmor -o /etc/apt/keyrings/docker.gpg
             apt-get update
             apt-get install --only-upgrade -y docker-ce docker-ce-cli containerd.io
         fi