postgresql: Disable 2 failing tests on musl

[nh2]

Motivation for this change

Make postgres tests not break build on musl.

See here from Alpine:

• https://git.alpinelinux.org/aports/tree/main/postgresql/disable-broken-tests.patch?id=6d7d32c12e073a57a9e5946e55f4c1fbb68bd442

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 nix-review --run "nix-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)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

Notify maintainers

cc @ocharles @thoughtpolice @danbst @globin

cc @matthewbauer