Utilize iloc rather than integer keys

[sco1]

Starting with Pandas v2.1.0 we start to get deprecation warnings on some of our data access, e.g.:

FutureWarning: Series.__getitem__ treating keys as positions is deprecated. In a future version, integer keys will always be treated as labels (consistent with DataFrame behavior). To access a value by position, use `ser.iloc[pos]`
    assert log_obj.press_temp["press_alt_m"][0] == pytest.approx(136.20, abs=1e-2)

This may only be in the test code but should check over the rest of the codebase