haproxy: 1.7.8 -> 1.7.9, download source via https

[fuzzy-id]

Motivation for this change

New version available (1.7.9). Also the site is now accessible via https.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option build-use-sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • Linux
• 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/)
• Fits CONTRIBUTING.md.

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[mention-bot]

@fuzzy-id, thanks for your PR! By analyzing the history of the files in this pull request, we identified @rbvermaa, @garbas and @pmahoney to be potential reviewers.