Extend support for Python 3.10

[santisoler]

Description

Python 3.10 is due to release on October 2021 and Fatiando libraries should support it too.
There's no much work to do so, we would need to expand the automated tests on CIs to Python 3.10, add 3.10 to the setup.py and check if every test pass.

This issue was inspired on @hugovk contribution to Pooch: fatiando/pooch#260

Apply changes to

Libraries:

• boule
• harmonica
• pooch
• verde

Further instructions

In order to solve this issue we need to start opening Pull Requests on each
repository listed above. Optionally, we can open Issues on each repository if
further discussion specific to that repository is needed.

Remember to mention this Issue on every Issue or Pull Request opened on each
repository for keeping a record by adding something like:

Related to fatiando/maintenance#15

A quick checklist:

1. Open an Issue on each repository listed above (optional). Mention this Issue
   on them.
2. Open a Pull Request on the same repository to tackle the Issue. Mention this
   Issue on them.
3. Check-off the repository on the list above once the Pull Request is merged.
4. Close this issue when all items are checked-off.

We want your help

We know that maintenance tasks are very demanding, so we don't expect a single
person to tackle this issue by themselves. Any help is very welcomed, so please
comment below that you want to take care of the changes on any repository and
we will assign it to you.

[hugovk]

I can help out, I'll start from the bottom of the list and work up!

[hugovk]

I'm not familiar with enough with Conda for most of them, but I'm looking at boule and erizo.

[santisoler]

Thanks a lot for the help @hugovk! Don't worry about Conda, CIs will handle the testings. Hopefully they won't complain about anything 🤞🏼 . So don't bother to locally test each library with conda if it's too troublesome for you.

[hugovk]

boule can be checked off the list: fatiando/boule#87

[hugovk]

This issue can be closed now, harmonica and verde now support 3.10:

• Extend support for Python 3.10 harmonica#240
• Add support for Python 3.10 verde#346

Next up: 3.11, released in October 2022 ;)

[leouieda]

Thanks @hugovk! Always appreciated 🙂