fix: require python >=3.7 again (the python 3.9 dependency was unnecessary)

[dlaehnemann]

Description

The respective bug was introduced with PR #2341, so it exists starting with version 7.30.2. Also see issue #2369 and PR #2370 for further context.

This code from PR #2341 seems to get run every time a conda environment is used:

snakemake/snakemake/__init__.py

Lines 8 to 9 in 13b5d4d

	if sys.version_info < (3, 9):
	raise ValueError("Snakemake requires at least Python 3.9.")

Thus, any conda environment in a rule with an older python version included, will trigger a:

  File "/opt/conda/envs/snakemake/lib/python3.11/site-packages/snakemake/__init__.py", line 9, in <module>
    raise ValueError("Snakemake requires at least Python 3.9.")
ValueError: Snakemake requires at least Python 3.9.

This would preclude snakemake from running any software that needs an older python version, so this is clearly an unwanted side-effect. But I am not sure how to fix this.

Currently, this PR is only a minimal example test to trigger this behaviour in the CI tests. Hopefully, this will make debugging it quicker for @johanneskoester (or someone else?).

QC

• The PR contains a test case for the changes or the changes are already covered by an existing test case.
• The documentation (docs/) is updated to reflect the changes or this is not necessary (e.g. if the change does neither modify the language nor the behavior or functionalities of Snakemake).

[github-actions]

Please format your code with black: black snakemake tests/*.py.

[dlaehnemann]

A quick workaround for anybody getting this bug, until it is fixed: Downgrade your snakemake to <=7.30.1.

[dlaehnemann]

So, this bug gets triggered in the Windows CI already, right here is the actual error message:
https://github.com/snakemake/snakemake/actions/runs/5690154966/job/15423010580?pr=2372#step:6:526

Currently rerunning the Linux CI, as this failed on slurm cluster creation earlier in the tests.

[dlaehnemann]

The Linux CI failure seem to be an unrelated and obscure error, where the general GitHub Actions runner is Ubuntu 22.04.2, but the slurm setup tries to download Ubuntu 22.04.1 packages, with the respective version not available on the Azure Ubuntu package mirror. I have no clue, why these versions would be out of sync...

[dlaehnemann]

Here's a related PR for the Linux CI failure with the slurm setup #2377 .

[johanneskoester]

I expect this to be fixed with the changes in #2305. However, that will become Snakemake 8.0. I'll think about a fix for the 7.x series, in order to have a final release that works.

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

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