sage.quadratic_forms: Fix use of staticmethod for Python < 3.10

[mkoeppe]

📚 Description

Fixes #35557

📝 Checklist

• The title is concise, informative, and self-explanatory.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation accordingly.

⌛ Dependencies

[github-actions]

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[kwankyu]

works well on sage with python 3.9.

[kwankyu]

Nothing related with this PR, but out of curiosity, do you use the number to search for labels like "critical / 2"?

[mkoeppe]

I think I use it about half of the time. Pretty rare event to use priority labels (in particular, Volker's merging script does not pay attention to them), so it's not hardwired in my fingers yet.
Also typing "s:" to see the status labels has not become a proper habit yet. I find myself typing "need" or "revi" and then click to change labels.

[mkoeppe]

Thanks for the review!

[kwankyu]

Also typing "s:" to see the status labels has not become a proper habit yet. I find myself typing "need" or "revi" and then click to change labels.

I see. I just scroll to the label in the list :-)

Thanks.