nixos/listmonk: fix db settings type

[eclairevoyant]

Things done

see #438619, #438558 for context and a similar fix.

• Built on platform:
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• Tested, as applicable:
  • NixOS tests in nixos/tests.
  • Package tests at passthru.tests.
  • Tests in lib/tests or pkgs/test for functions and "core" functionality.
• Ran nixpkgs-review on this PR. See nixpkgs-review usage.
• Tested basic functionality of all binary files, usually in ./result/bin/.
• Nixpkgs Release Notes
  • Package update: when the change is major or breaking.
• NixOS Release Notes
  • Module addition: when adding a new NixOS module.
  • Module update: when the change is significant.
• Fits CONTRIBUTING.md, pkgs/README.md, maintainers/README.md and other READMEs.

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[eclairevoyant]

@MarcelCoding @Stunkymonkey might be interested to review?

[Stunkymonkey]

i ran also nix-build . -A nixosTests.listmonk which was successful. so LGTM

[MarcelCoding]

Sorry, can't realy help here. Migrated to mailman3 long time ago ;) Don't know the semantics of databaseSettingsOpts etc.

[eclairevoyant]

Basically it was always a type error, because freeformType should always be attrsOf/lazyAttrsOf something, as a submodule with inner mkOptions is by nature returning an attrset.

Prior to some other module system changes, the module system was silently just dealing with the type mismatch by not-merging definitions; now it's an actual error. Hence end-users would encounter the error and be unable to eval their configs much less build them, without this fix.

I found a few dozen other similar cases, I'll try to do a treewide at some point...

[eclairevoyant]

@ofborg test listmonk