make html in doc/ fails because of missing "import os"

[gl-yziquel]

Just checked out DEAP from git HEAD.

make html in docs/ folder fails with this error message:

mini-me@virtucon ~/h/c/deap (master)> cd doc
mini-me@virtucon ~/h/c/d/doc (master)> make html
PYTHONPATH=/home/mini-me/home/cellar/deap/doc/../ sphinx-build -b html -d _build/doctrees   . _build/html
Running Sphinx v7.2.2

Configuration error:
There is a programmable error in your configuration file:

Traceback (most recent call last):
  File "/home/mini-me/.pyenv/versions/3.12.2/lib/python3.12/site-packages/sphinx/config.py", line 358, in eval_config_file
    exec(code, namespace)  # NoQA: S102
    ^^^^^^^^^^^^^^^^^^^^^
  File "/home/mini-me/home/cellar/deap/doc/conf.py", line 134, in <module>
    tree = os.getenv('GITHUB_COMMIT')
           ^^
NameError: name 'os' is not defined. Did you forget to import 'os'

make: *** [Makefile:34: html] Error 2