Preparing for GAP 4.13.0

[fingolfin]

It's been half a year since GAP 4.12.0, so time to think about GAP 4.13.0.

The milestone for 4.13.0 currently still lists 37 issues. I will address a few of them and probably punt most of the others, but if someone would like to tackle any of them, be my guest :-).

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Besides the various changes in PRs here, I am in particular happy about the continuing improvement of our package ecosystem. I think we'll be able to close these issues for 4.13 (which could be covered in the release notes, as it'll be relevant for downstream packagers)

• Distributed packages without a License field #4802
• Packages: get all packages to support ./configure --with-gaproot=PATH #5303
• buildsys: stop installing ${includedir}/gap/src once no package needs it anymore #5361

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Some release specific issues that would be great to resolve once and for all:

• Make generate_release_notes.py much faster #5001
• Enhance generate_release_notes.py to also report added/removed/update packages #5004
• Release CI once again failed to build windows executables #5285

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I will update this issue description with further details as necessary (or rather: as I feel is helpful for preparing the release)

[fingolfin]

I'd love to get in a new release for Alnuth (see gap-packages/alnuth#29) and polycyclic, but I might not be able for 4.13.0; but perhaps during GAP Days, for 4.13.1 ?

[fingolfin]

Nothin