plantuml: downgrade graphviz to 2.32

[nightkr]

Motivation for this change

PlantUML discourages Graphviz 2.39+ due to rendering bugs: see http://plantuml.com/faq (heading: "Which version of Graphviz should I use ?")

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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[erictapen]

@oxij is doing an effort atm to move package configurations from all-packages.nix into the package definitions itself (see e.g. #56088). Maybe it would be a better suited to put your change into pkgs/tools/misc/plantuml/default.nix?

[oxij]

There's no consensus on moving package defaults (as opposed to option defaults) to the expressions themselves. I think we should, but changes like these are in progress ATM, so I think this PR is okay as is for now.