Allow for existing group

Docker/Dockerfile

@@ -6,6 +6,6 @@ RUN DEBIAN_FRONTEND=noninteractive apt update && apt install -y build-essential
 ARG USER=docker
 ARG UID=1000
 ARG GID=1000
-RUN groupadd -g ${GID} docker && useradd -ms /bin/bash ${USER} -u ${UID} -g ${GID}
+RUN groupadd -f -g ${GID} docker && useradd -ms /bin/bash ${USER} -u ${UID} -g ${GID}
 
 USER ${UID}:${GID}