Add pendulum to dockerfile

[sukoneck]

This change fixes docker builds, which are failing due to the latest release of pendulum:

...
> [6/6] RUN airflow db init > /dev/null:                                                             
0.400 Traceback (most recent call last):                                                              
0.400   File "/usr/local/lib/python3.11/site-packages/airflow/settings.py", line 55, in <module>
0.400     TIMEZONE = pendulum.tz.timezone(tz)
0.400                ^^^^^^^^^^^^^^^^^^^^^^^^
0.400 TypeError: 'module' object is not callable
...

[sukoneck]

bump 🙏