Ubuntu ARM image missing Python package requests

[xuganyu96]

This causes weekly tests to fail, such as here.

_________________ ERROR collecting tests/test_acvp_vectors.py __________________
ImportError while importing test module '/home/runner/work/liboqs/liboqs/tests/test_acvp_vectors.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
tests/test_acvp_vectors.py:8: in <module>
    import requests
E   ModuleNotFoundError: No module named 'requests'
======= 333 passed, 1807 skipped, 15 xfailed, 1 error in 2787.99 seconds =======