[dependencies] Upgrade pymongo>4 and motor>3.

[alexandervaneck]

Hi @lafrech 👋

Thank you for maintaining umongo, a product we maintain depends on it! 🙇

Lately it's come to our attention that we're not using the latest pymongo version and this is due to umongo[motor] being pinned to motor>2,<3.

Are you aware of a specific reason why motor is pinned <3?
It started supporting pymongo>4 after 3.0 unfortunately.

If it helps I can open a PR to investigate motor 3.x support in umongo 🙌

[alexandervaneck]

I now see that umongo (optionally) depends on txmongo which also doesn't support pymongo>4. 🤔

twisted/txmongo#278 (comment)

Looks like this was discussed before: #381

[alexandervaneck]

Alright - I opened a PR to allow motor>3 and all tests pass. I did not check compatibility with txmongo since it could be seen as unrelated to motor support for pymongo.

I look forward to a review 🙇 Let me know how best to merge this.

[lafrech]

Hi. Than you for your interest in umongo.

I think it is good practice to pin major versions so that everything does break when a new major dependency version is published. I totally agree with adding motor >=3,<4 support. Thanks for the PR.

Indeed this is independent from txmongo support (#381).