Use string type annotations for Python 3.11 not 3.10

[frenzymadness]

PEP 563 has been postponed to Python 3.11
https://mail.python.org/archives/list/python-dev@python.org/thread/CLVXXPQ2T2LQ5MP2Y53VVQFCXYWQJHKZ/

Another possibility is to revert this commit: 8a278a1

It's basically up to you to decide whether you want to be ready for Python 3.11 and keep this in the codebase for a year and a half.

And finally, the last possibility might be to use from __future__ import annotations to enable the new feature for Python 3.7+.

[codecov]

Codecov Report

Merging #420 (ebac5f5) into master (6e0f571) will not change coverage.
The diff coverage is n/a.

@@ Coverage Diff @@## master #420 +/- ##
=======================================
Coverage 91.76% 91.76% =======================================
Files 4 4 Lines 668 668 Branches 136 136 =======================================
Hits 613 613 Misses 34 34 Partials 21 21 

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[ogrisel]

LGTM. Maybe we want to explore the support for 3.7+ using the from __future__ pattern but I am not sure about the implications.

[ogrisel]

We probably need to update the CI config to include a nightly build to test explicitly the future 3.11 from the the main branch of Python and the 3.10 pre-release separately.

[pierreglaser]

Python 3.11 is now tested in nightly while Python 3.10 is tested in the 3.10-dev entry.
Now, testing against nightly fails, because of some change in the code constructor.

[pierreglaser]

At the time when I am writing this message, the change in the code constructor has still an uncertain future. As discussed here: https://bugs.python.org/issue40222, the change might be reverted for the sake of backward compatibility, although it is not sure yet. For this reason, I suggest we make the CI entry using Python nightly (3.11 right now) optional until a final solution to the previous issue is decided.

[pierreglaser]

(Just making that labelling this PR using the python-nightly label triggers a run of the python-nightly CI entry)

[pierreglaser]

(Skipping an entry in the changelog since this PR only affected tests and CI config)

EDIT: actually, a changelog entry was added for #400, So we need to update it since this PR updates changes from #400.