fix: correct workspace_dir path resolution

[r83575]

This PR updates the way workspace_dir is resolved in the jetson and ml_cpu Docker scripts.

Changes

• Replaced path resolution logic to use realpath consistently from script location.
• Ensures env_dir always points to the correct absolute path, regardless of execution context.

This fix ensures the Docker build uses the correct environment path.

Notes

• No other logic or behavior was changed.
• Tested on both jetson and ml_cpu environments.