Use latest year available by default

[rafapereirabr]

By default, functions should read the data from the latest year available. This is a big change planned for the next update of {geobr}. Users concerned with the reproducibility of their code would explicitly pass the year argument.

[rafapereirabr]

This change has been implemented in the dev version of {geobr} R in 0359469.

The change still needs to be implemented in {geobr} Python.