pulseaudio: fix evaluation with Nix 2.3
pulseaudio: fix evaluation with Nix 2.3

Path interpolation syntax has been introduced in Nix 2.4 and may not be
used in nixpkgs which needs to be able to be evaluated with Nix 2.3.

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs