Make pass regardless of build setup and dependencies

Author: AdamGS

datafusion/expr/Cargo.toml

@@ -66,3 +66,6 @@ sqlparser = { workspace = true, optional = true }
 ctor = { workspace = true }
 env_logger = { workspace = true }
 insta = { workspace = true }
+# Makes sure `test_display_pg_json` behaves in a consistent way regardless of
+# feature unification with dependencies
+serde_json = { workspace = true, features = ["preserve_order"] }