harfbuzz: fix checkPhase on sandboxed Darwin

The native_coretext_variations test in harfbuzz's test suite depends on
the system-provided fonts and will fail if they cannot be read [1]. Add
/System/Library/Fonts to __impureHostDeps (which updates the sandbox
profile) to resolve the test failure on Darwin.

[1]: https://gist.github.com/al3xtjames/c6f5f2e1217c9e8607ac9d70ce333e0c#file-harfbuzz-11-2-1-drv-log-L789-L812

pkgs/by-name/ha/harfbuzz/package.nix

@@ -103,6 +103,11 @@ stdenv.mkDerivation (finalAttrs: {
 
   doCheck = true;
 
+  # test_native_coretext_variations depends on the system fonts.
+  __impureHostDeps = lib.optionals stdenv.hostPlatform.isDarwin [
+    "/System/Library/Fonts"
+  ];
+
   # Slightly hacky; some pkgs expect them in a single directory.
   postFixup = lib.optionalString withIcu ''
     rm "$out"/lib/libharfbuzz.* "$dev/lib/pkgconfig/harfbuzz.pc"