Support Python 3.11 and remove Python 3.7 support

[ptsavol]

This will also remove Python 3.7 support to be consistent with spinetoolbox, and spine-items packages.

Related to issue Spine-project/Spine-Toolbox#1896

Checklist before merging

• [ ] Documentation (also in Toolbox repo) is up-to-date
• [ ] Release notes in Toolbox repo have been updated
• [x] Unit tests have been added/updated accordingly
• [x] Code has been formatted by black
• [x] Unit tests pass

[codecov-commenter]

Codecov Report

Base: 74.53% // Head: 74.53% // No change to project coverage :thumbsup:

Coverage data is based on head (5dc2307) compared to base (3b6a6c8). Patch has no changes to coverable lines.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #201 +/- ## ======================================== Coverage 74.53% 74.53% ======================================== Files 77 77 Lines 12002 12002 Branches 2347 2594 +247 ======================================== Hits 8946 8946 Misses 2591 2591 Partials 465 465 ``` Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Spine-project). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Spine-project)

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