openvpn3: 20 -> 21

[jfly]

Here's the changelog for openvpn3-linux: https://github.com/OpenVPN/openvpn3-linux/releases/tag/v21
I also upgraded openvpn3-core from 3.7.2 to 3.8.4: OpenVPN/openvpn3@release/3.7.2...release/3.8.4

Description of changes

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 24.05 Release Notes (or backporting 23.05 and 23.11 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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[jfly]

Result of nixpkgs-review run on x86_64-linux 1

1 package built:

• openvpn3

[KFearsoff]

Thank you for the contribution. LGTM!

An unfortunate caveat is that the OpenVPN3 part of the CLI is broken unless someone figures out the build (I couldn't) or until we get v22. Here is the tracking issue: #235986

[jfly]

It turns out there are DNS lookup domain related bugs in v21 that make it so that I don't want to use it myself. Between that and the glib issues, I guess it's best for nixpkgs to just wait for openvpn v22. Closing this PR.