Permission denied trying to mkdir in build with jenkins and kubernetes - docker

Question

I need to create a folder in one of the stages of a build in jenkins, but I'm getting a permission error when it tries to run mkdir.
dockerfile:
FROM debian:latest
USER root
WORKDIR /root
RUN apt-get update
RUN apt-get upgrade -y
RUN apt-get install -y gnupg2
RUN DEBIAN_FRONTEND="noninteractive" apt install -y apt-transport-https ca-certificates software-properties-common curl git jq wget unzip
RUN curl -s https://storage.googleapis.com/golang/go1.15.6.linux-amd64.tar.gz| tar -v -C /usr/local -xz
RUN export PATH=$PATH:/usr/local/go/bin
#
# Docker
#
RUN curl -fsSL https://download.docker.com/linux/debian/gpg | apt-key add -
RUN apt-key fingerprint 0EBFCD88
RUN add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/debian $(lsb_release -cs) stable"
RUN apt-get update
RUN apt-get install -y docker-ce docker-ce-cli containerd.io
ENV PATH=$PATH:/usr/local/go/bin
RUN export PATH=$PATH:/usr/local/go/bin
WORKDIR /app/src/
Stage of Jenkinsfile:
stage('Restore') {
try {
timeout(time: 10, unit: 'MINUTES') {
dir('.') {
sh "mv * /root/go/src/Proj/"
}
dir('/root/go/src/Proj/') {
sh "mkdir ./${repoName}"
}
}
} catch (Exception err) {
cleanWS()
error("[FAILED]: " + err.getMessage())
}
}
The mv command works fine, but when it comes to mkdir, it gives me this error:
java.nio.file.AccessDeniedException: /root/go/src
Does anyone know how could I set this permission?