sage: 8.6 -> 8.7

[timokau]

Motivation for this change

Here's the next round. Tracking the betas and rc's until the next release (if I get around to it).

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Assured whether relevant documentation is up to date
• Fits CONTRIBUTING.md.

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[timokau]

Just as a status update: sage 8.7 has been released, but the update in nix is blocked by #56911 which is in turn blocked by gmpy2/gmpy2#199.

Resolved

[timokau]

The gmpy2 beta release seems to be a while off yet. I don't want to hold back the sage release any longer and gmpy2 only has a handful of reverse dependencies. I'll merge if a final nix-review passes for this PR.

[timokau]

Next iteration in #59989.