doctester: Check for consistency of # optional annotations

[mkoeppe]

📚 Description

For example:

sage -t --long --random-seed=52927571004392838159040103596363721016 src/sage/rings/function_field/function_field.py
**********************************************************************
File "src/sage/rings/function_field/function_field.py", line 40, in sage.rings.function_field.function_field
Warning: Variable 'L' referenced here was set only in doctest marked '# optional - sage.rings.finite_rings sage.rings.function_field'
    S.<t> = L[]                                                                   # optional - sage.rings.finite_rings

Resolves #35401

📝 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

[kwankyu]

It works well.

I was a bit concerned that this would slowdown doctesting slightly, but the concern seems imaginary.

[mkoeppe]

Thank you!

[vbraun]

Test fail

It seems that # long time tests are not covered by the CI, is that true?

[mkoeppe]

Test fail

Sorry about this, will fix.

It seems that # long time tests are not covered by the CI, is that true?

Yes, that's currently true.

#35652 changes this (by first running a fast incremental build/test, then running a full build of the Sage and ptest --long)

[vbraun]

Tests still fail. Thats two strikes. Please don't make it three.

[mkoeppe]

Sorry about this. Fixed now.

[github-actions]

Documentation preview for this PR (built with commit ac1f1fe) is ready! 🎉