tests: fix test-demandimport.py on Python 3.9
Starting with Python 3.9, importing importlib.resources (indirectly) imports
the zipfile module. Therefore, the module is not suitable for the test.
Instead, we can use the ftplib module, which is very unlikely to be imported
during the test run.
Added signature for changeset
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Added tag 5.5.1 for changeset
f62bb5d07848