do not run unit tests on Python 3.5

[branfosj]

From https://github.com/easybuilders/easybuild-easyblocks/actions/runs/9030743894/job/24821557865?pr=3311

Could not fetch URL https://pypi.python.org/simple/pip/: There was a problem confirming the ssl certificate: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:728) - skipping
Error: Could not find a version that satisfies the requirement pip (from versions: )
Error: No matching distribution found for pip
Error: The process '/usr/bin/bash' failed with exit code 1

[ocaisa]

LGTM