rootless script does not work on $(id -un) that returns backslash

• This is a bug report
• This is a feature request
• I searched existing issues before opening this one

Expected behavior

Following the documentation https://docs.docker.com/engine/security/rootless/
the command below should enable the rootless mode for docker

curl -fsSL https://get.docker.com/rootless | sh

Actual behavior

the script fail on line
if ! grep "^$(id -un):\|^$(id -u):" /etc/subuid >/dev/null 2>&1; then

due to the presence of a backslash character in the output of the command "id -un"

Steps to reproduce the behavior

create and use a user with a backslash in his name
launch the command line :
curl -fsSL https://get.docker.com/rootless | sh

I have try to fix the lines for subuid and subgid detection using sed but it is not sufficient
grep "^$(id -un | sed -e "s/[\]/\\\\\\\\/g"):" /etc/subuid

Output of docker version:

(paste your output here)

Output of docker info:

(paste your output here)

Additional environment details (AWS, VirtualBox, physical, etc.)

aws workspace
NAME="Amazon Linux"
VERSION="2"
ID="amzn"
ID_LIKE="centos rhel fedora"
VERSION_ID="2"
PRETTY_NAME="Amazon Linux 2"

Start with the rootless installer invoked by curl -fsSL https://get.docker.com/rootless | sh, focusing on the /etc/subuid check shown in the report and the corresponding subgid detection. Reproduce it with a user whose name contains a backslash and verify that rootless installation completes successfully without breaking the existing checks.