delta: update skipped tests on Darwin

0.18.0 replaced the `test_diff_same_non_empty_file` test with
`test_diff_real_files`[^1], which similarly fails on Darwin when the
sandbox is enabled.[^2]. Update `checkFlags` to skip the new test on
Darwin.

[^1]: 5c53c5e3d9 (diff-46662042aa1e2ba8561f9c545e204a30c8fe4450296390453f3098263fdb402eL98)
[^2]: https://gist.github.com/al3xtjames/fa1a2d5f6dd60cbea7031f4bb7014e12

pkgs/applications/version-management/delta/default.nix

@@ -50,7 +50,9 @@ rustPlatform.buildRustPackage rec {
   dontUseCargoParallelTests = true;
 
   checkFlags = lib.optionals stdenv.isDarwin [
-    "--skip=test_diff_same_non_empty_file"
+    # This test tries to read /etc/passwd, which fails with the sandbox
+    # enabled on Darwin
+    "--skip=test_diff_real_files"
   ];
 
   meta = with lib; {