sagemathgh-36025: Use `# optional - gap_package_grape` etc. instead of `# optional - gap_packages`
    
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The Sage distribution has an optional SPKG `gap_packages`, which is a
collection of GAP packages used by parts of Sage.
The doctests that uses these packages are currently marked `# optional -
gap_packages`. Here we switch to using more specific feature tags. These
more specific features are tested dynamically, which works outside of
the Sage distribution.
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- Depends on sagemath#36017
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URL: sagemath#36025
Reported by: Matthias Köppe
Reviewer(s): David Coudert

sagemathgh-36034: Fix block-scoped doctest tags with `\` line continuations
    
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Fixes
sagemath#36033 (comment)
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### ⌛ Dependencies

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- Depends on sagemath#36025 (merged here)

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URL: sagemath#36034
Reported by: Matthias Köppe
Reviewer(s): Kwankyu Lee, Matthias Köppe