Jenkins Git Plugin Cannot Obtain ~/. Ssh/Config File

I'm using helm Jenkins chart

Pod template for agent

        jenkins:
          clouds:
            - kubernetes:
                name: "kubernetes"
                serverUrl: ""
                skipTlsVerify: true
                namespace: "jenkins"
                jenkinsUrl: ""
                jenkinsTunnel: "jenkins-agent:50000"
                containerCapStr: 42
                maxRequestsPerHostStr: 64
                retentionTimeout: 5
                connectTimeout: 10
                readTimeout: 20

                templates:
                  - name: "test"
                    label: "jenkins-agent"
                    # Enable whether the POD Yaml is displayed in each build log or not, `true` by default.
                    showRawYaml: true
                    volumes:
                      - hostPathVolume:
                          mountPath: "/var/run/docker.sock"
                          hostPath: "/var/run/docker.sock"

                    containers:
                      - name: "backend"
                        image: "mycustomimage"
                        privileged: true
                        alwaysPullImage: true
                        command: "/bin/sh -c"
                        args: "cat"
                        workingDir: "/home/jenkins/agent"
                        ttyEnabled: true
                        resourceRequestCpu: "500m"
                        resourceRequestMemory: "1Gi"
                        resourceLimitCpu: "2000m"
                        resourceLimitMemory: "2Gi"
                    imagePullSecrets:
                      - name: "registrysecret"

in the end of my dockerfile for "mycustomimage"

base image is debian:buster

RUN useradd -u $JENKINS_USER_UID $JENKINS_USER -m -d $JENKINS_HOME -G docker
USER $JENKINS_USER
RUN mkdir $JENKINS_HOME/.ssh && ssh-keyscan ssh.github.com > $JENKINS_HOME/.ssh/known_hosts
RUN echo "Host github.com\n    Hostname ssh.github.com\n   Port 443\n   User git" > $JENKINS_HOME/.ssh/config

Issue is really tricky.

1. If I'm using pipeline from SCM Jenkins can easily obtain JenkinsFile from the repo(that checkout is going through jenkins-master pod for sure) Than inside JenkinsFile I have next

pipeline {
    agent {
        node { label 'jenkins-agent'}
    }
 ....
stage('Source Code Checkout') {
            steps {
                container('backend') {
                    git branch: 'main',
                        credentialsId: 'git_user_ssh',
                        url: '[email protected]:org/repo.git'

Jenkins always returns

[2022-08-27T22:03:06.716Z] stderr: ssh: connect to host github.com port 22: Connection timed out
[2022-08-27T22:03:06.716Z] fatal: Could not read from remote repository.
[2022-08-27T22:03:06.716Z] 
[2022-08-27T22:03:06.716Z] Please make sure you have the correct access rights
[2022-08-27T22:03:06.716Z] and the repository exists.

Checking user in container

Exec into pod and try same

as you can see ssh command obtains config and it is trying to clone repo using 443 port(not 22 as jenkins). Then I put private key in .ssh folder and clone works perfectly. That means there isn't network issue.

2. Trying to clone in "Pipeline script" with git command in sh

        stage('Source Code Checkout') {
            steps {
                container('backend') {
                    script{
                       sh "git clone [email protected]:org/repo.git"

result

3. Trying to clone via GitSCM plugin in "Pipeline script"

        stage('Source Code Checkout') {
            steps {
                container('backend') {
                    git branch: 'main',
                        credentialsId: 'git_user_ssh',
                        url: '[email protected]:org/repo.git'

result

jfyi

Could someone please explain to me the cause of problem? Or how to specify port while cloning repo through Jenkins. Thanks in advance.

Jenkins home as was requested

                container('backend') {
                    script{
                        sh "cd $JENKINS_HOME || true"
                        sh """cd ~
                            pwd
                            ls -la
                        """