setup: fix unbound SUDO_USER variable when running as root in Docker

[Divinesoumyadip]

When setup.sh is run directly as root , which is standard in Docker containers and CI/CD pipelines so,$SUDO_USER is never set. Because the script uses set -euo pipefail, the -u flag causes the script to crash immediately on any unbound variable reference.

Two lines were affected:

Line 28: bash sudo -u $SUDO_USER git submodule update --init --recursive

Line 42: sudo -u $SUDO_USER "$DIR/etc/DependencyInstaller.sh" -common -prefix="$DIR/dependencies"

When $SUDO_USER is empty, sudo -u consumesgit(or the script path) as the username and crashes with:

sudo: unknown user: git 
sudo: error initializing audit plugin sudoers_audit

To resolve this, the script now checks if $SUDO_USER is set before attempting to use it. If the variable is set (indicating the script was invoked via sudo), it drops privileges to the original user as intended. However, if it is empty (indicating the script is running natively as root), it simply runs the command directly without the sudo -u flag. The macOS paths were already handled correctly by #4023, so this PR completes the fix for the remaining Linux and Docker environments.

[Divinesoumyadip]

@maliberty @luarss could you approve the workflows to run CI? Happy to address any review feedback.

[luarss]

this nested loop causes lots of repeated code. is a helper function possible here?

[Divinesoumyadip]

this nested loop causes lots of repeated code. is a helper function possible here?

Done! Refactored to use a run_as_user() helper function that handles both cases drops privileges to the original user when invoked via sudo, and runs directly when already root. Removes the repeated pattern across both submodule and dependency installer calls.

[github-actions]

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