unity-builder: v2.2.0 breaks builds on Linux machines

Hello. It seems that v2.2.0 release broke Android/iOS builds on Linux machines.

Bug description

Run a CI in an ordinal manner.

GitHub Actions log says:

Run game-ci/unity-builder@v2
  with:
    versioning: None
    customImage: custom-editor:2021.3.11f1-ios-1.0.1
    projectPath: Unity/develop
    buildMethod: OurOwnBuildMethod
    customParameters: -stage Test
    targetPlatform: iOS
    unityVersion: auto
    androidAppBundle: false
    androidSymbolType: none
    sshAgent: public
    awsBaseStackName: game-ci
    cloudRunnerCluster: local
    kubeVolumeSize: 5Gi
    watchToEnd: true
    cacheUnityInstallationOnMac: false

/home/ubuntu/bin/docker run --workdir /github/workspace --rm --env UNITY_LICENSE --env UNITY_SERIAL=SERIAL_NUMBER --env UNITY_VERSION=2021.3.11f1 --env PROJECT_PATH=Unity/develop --env BUILD_TARGET=Android --env BUILD_NAME=Android --env BUILD_PATH=build/Android --env BUILD_FILE=Android.apk --env BUILD_METHOD=OurOwnBuildMethod --env VERSION=none --env ANDROID_VERSION_CODE=0 --env ANDROID_EXPORT_TYPE=androidPackage --env ANDROID_SYMBOL_TYPE=none --env CUSTOM_PARAMETERS=-stage Test --env GITHUB_REF=some/ref --env GITHUB_SHA=d5c7c793f9aa98253d76da0d51bcf4f1108cc67d --env GITHUB_REPOSITORY=ourrepo --env GITHUB_ACTOR=Somebody --env GITHUB_WORKFLOW=Build TEST/DEV/BOYOD App --env GITHUB_EVENT_NAME=workflow_dispatch --env GITHUB_ACTION=__self --env GITHUB_EVENT_PATH=/home/ubuntu/actions-runner/_work/_temp/_github_workflow/event.json --env RUNNER_OS=Linux --env RUNNER_TOOL_CACHE=/home/ubuntu/actions-runner/_work/_tool --env RUNNER_TEMP=/home/ubuntu/actions-runner/_work/_temp --env RUNNER_WORKSPACE=/home/ubuntu/actions-runner/_work/ourrepo --env SSH_AUTH_SOCK=/ssh-agent --env UNITY_SERIAL --env GITHUB_WORKSPACE=/github/workspace --env SSH_AUTH_SOCK=/ssh-agent --volume /home/ubuntu/actions-runner/_work/_temp/_github_home:/root:z --volume /home/ubuntu/actions-runner/_work/_temp/_github_workflow:/github/workflow:z --volume /home/ubuntu/actions-runner/_work/ourrepo/ourrepo:/github/workspace:z --volume /home/ubuntu/actions-runner/_work/_actions/game-ci/unity-builder/v2/dist/default-build-script:/UnityBuilderAction:z --volume /home/ubuntu/actions-runner/_work/_actions/game-ci/unity-builder/v2/dist/platforms/ubuntu/steps:/steps:z --volume /home/ubuntu/actions-runner/_work/_actions/game-ci/unity-builder/v2/dist/platforms/ubuntu/entrypoint.sh:/entrypoint.sh:z --volume /home/ubuntu/actions-runner/_work/_actions/game-ci/unity-builder/v2/dist/unity-config:/usr/share/unity3d/config/:z --volume public:/ssh-agent --volume /home/runner/.ssh/known_hosts:/root/.ssh/known_hosts:ro custom-editor:2021.3.11f1-android-1.0.1 /bin/bash -c /entrypoint.sh
docker: Error response from daemon: error while creating mount source path '/home/runner/.ssh/known_hosts': mkdir /home/runner: permission denied.
Error: The process '/home/ubuntu/bin/docker' failed with exit code 126
Run game-ci/unity-builder@v2

How to reproduce

• Launch an EC2/Ubuntu instance and setup a rootless Docker in it
• Register the instance as a GItHub Actions self-hosted runner and trigger an Android / iOS build inside Linux instance

Expected behavior

Builds fine.

Additional details

This is because sshAgent has a default value since v2.2.0: https://github.com/game-ci/unity-builder/commit/0efa1855a3c37ab64c3a9e221a939a967932923c#diff-1243c5424efaaa19bd8e813c5e6f6da46316e63761421b3e5f5c8ced9a36e6b6R89

This might be avoided by explicitly setting sshAgent: '' in your with params (not confirmed).