nixosTests.forgejo{,-lts}: migrate to runTest

[emilylange]

This is part of the bigger handleTest deprecation.

See #386873 and #383870 (7e3c668).

Figured we can drop the listToAttrs (map makeForgejoTest supportedDbTypes) and just list them one by one to increase readability and not having to awkwardly pass listToAttrs to the import in all-tests.nix.
If someone disagrees with this or has some better idea, let me know. Open to change it.

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/)
• 25.05 Release Notes (or backporting 24.11 and 25.05 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.

[adamcstephens]

x86

➜ nom-build -A forgejo-lts.passthru.tests -A forgejo.passthru.tests
Finished at 07:54:42 after 38s
/nix/store/srxn3afs7hlrky1nx2scgblib50l8rbq-vm-test-run-forgejo-mysql
/nix/store/95n6qmakasiiwzc971sjwib6r1l2m9sy-vm-test-run-forgejo-postgres
/nix/store/09rxvh866mi1hpb1378ivsxpxsb76mxx-vm-test-run-forgejo-sqlite3
/nix/store/c2vbqlzxqs9861j8qa6f7zjqqi7r808c-vm-test-run-forgejo-mysql
/nix/store/y5zzzgkpvb370fg1x5jgwqqyxff9mrvm-vm-test-run-forgejo-postgres
/nix/store/pnkhxpks06vy9jyr93i3r8kxkm95fyhm-vm-test-run-forgejo-sqlite3