Pandas warning: Calling int on a single element Series is deprecated and will raise a TypeError

[hyanwong]

Short description of the problem:
importing stdpopsim under pandas 2.0.1 results in a warning

How to reproduce the problem:

Python 3.10.10 | packaged by conda-forge | (main, Mar 24 2023, 20:17:34) [Clang 14.0.6 ] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import stdpopsim
/Users/yan/mambaforge/lib/python3.10/site-packages/stdpopsim/catalog/HomSap/demographic_models.py:158: FutureWarning: Calling int on a single element Series is deprecated and will raise a TypeError in the future. Use int(ser.iloc[0]) instead
  time=int(extended_GF.time.head(1) - 1), rate=0
mambaforge/lib/python3.10/site-packages/stdpopsim/catalog/HomSap/demographic_models.py:161: FutureWarning: Calling int on a single element Series is deprecated and will raise a TypeError in the future. Use int(ser.iloc[0]) instead
  time=int(extended_GF.time.tail(1) + 1), rate=0
>>> import pandas
>>> pandas.__version__
'2.0.1'

[nspope]

Looks like this got fixed by #1416 some time ago; code now reads https://github.com/popsim-consortium/stdpopsim/blame/b46b3d1dd9ad188d9a5bd6a36a90a9c69ae8f1a6/stdpopsim/catalog/HomSap/demographic_models.py#L146

and doesn't throw an error. Guess that this fix was post-0.2.0 release which is why Yan is picking up the error.