Revert Python 3.9 compatibility in test_iovs

The following discussion from !4931 (merged) should be addressed:

@clemenci started a discussion: (+2 comments)

I accidentally used a function introduced with Python 3.11, and we still use Python 3.9 (LCG 105c).

94b393eb fixes the problem but it should be reverted once we switch to LCG 106.

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