Remove use of s3-actions, use pip to install s3cmd

[atavism]

Using s3-actions/s3cmd breaks CI:

Run s3-actions/s3cmd@v1.4.0
error: externally-managed-environment

× This environment is externally managed
╰─> To install Python packages system-wide, try brew install
    xyz, where xyz is the package you are trying to
    install.
    
    If you wish to install a non-brew-packaged Python package,
    create a virtual environment using python3 -m venv path/to/venv.
    Then use path/to/venv/bin/python and path/to/venv/bin/pip.
    
    If you wish to install a non-brew packaged Python application,
    it may be easiest to use pipx install xyz, which will manage a
    virtual environment for you. Make sure you have pipx installed.

https://github.com/getlantern/lantern-client/actions/runs/8612860713/job/23602954471#step:20:1

This updates the release workflow to install s3cmd with pip instead.