python3.pkgs.rpy2: fix tests with pandas 1.x, 3.2.5 -> 3.2.6

[timokau]

Motivation for this change

The python3.pkgs.rpy2 build was broken by a recent update to pandas. A fix is already upstream and just needs to be backported. While I'm at it I also included a version bump to the latest released version.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• 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 nixpkgs-review --run "nixpkgs-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.