Auto merge of servo#29007 - yvt:patch/nix-pkgconfig, r=jdm

`etc/shell.nix`: Replace `pkgconfig` with `pkg-config`

`pkgconfig` is [an old name][1] of `pkg-config` that has been [completely removed][2] in a recent version of nixpkgs.

[1]: NixOS/nixpkgs#55094
[2]: NixOS/nixpkgs#192681

---
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [ ] These changes fix #___ (GitHub issue number if applicable)

---
- [ ] There are tests for these changes OR
- [x] These changes do not require tests because they don't affect the production code

Author: bors-servo

etc/shell.nix

@@ -18,7 +18,7 @@ clangStdenv.mkDerivation rec {
     rustup
 
     # Build utilities
-    cmake dbus gcc git pkgconfig which llvm autoconf213 perl yasm m4
+    cmake dbus gcc git pkg-config which llvm autoconf213 perl yasm m4
     (python3.withPackages (ps: with ps; [virtualenv pip dbus]))
   ] ++ (lib.optionals stdenv.isDarwin [
     darwin.apple_sdk.frameworks.AppKit