sagemathgh-40936: Require Python 3.12 or newer; remove outdated workarounds
    
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In line with [Spec 0](https://scientific-
python.org/specs/spec-0000/#drop-schedule), we remove support for Python
3.11. Many outdated patches/workarounds for these older (or even older)
Python versions are removed, but I cannot guarantee that I've found all
obsolete ones. Also CI tests for systems using Python 3.11 are removed.

For next years cleaning job:
- Change version in `pyproject.toml` and `build/pkgs/python3/spkg-
configure.m4`
- Search for `3.12`, `312`,`3,12`, `PY_VERSION`, `PY_MINOR_VERSION` and
`sys.version_info`

Similar PRs:
- sagemath#39251

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- [ ] I have linked a relevant issue or discussion.
- [ ] I have created tests covering the changes.
- [ ] I have updated the documentation and checked the documentation
preview.

### ⌛ Dependencies

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- sagemath#39163
    
URL: sagemath#40936
Reported by: Tobias Diez
Reviewer(s): Chenxin Zhong, Dima Pasechnik

Author: Release Manager

.devcontainer/onCreate-conda.sh

@@ -6,8 +6,8 @@ conda config --env --add channels conda-forge
 conda config --env --set channel_priority strict
 conda update -y --all --override-channels -c conda-forge
 conda install mamba=1 -n base -y
-mamba env create -y --file environment-3.11-linux.yml || mamba env update --file environment-3.11-linux.yml
+mamba env create -y --file environment-3.12-linux.yml || mamba env update --file environment-3.12-linux.yml
 conda init bash
 
 # Build sage
-conda run -n sage-dev pip install --no-build-isolation -v -v -e . --config-settings=build-dir="build/conda-cp311"
+conda run -n sage-dev pip install --no-build-isolation -v -v -e . --config-settings=build-dir="build/conda-cp312"