Add lint exception to make CI pass again

Author: umgefahren

Cargo.toml

@@ -31,3 +31,6 @@ bincode = "1"
 quickcheck = { version = "1.0.3", default-features = false }
 rand = "0.8.4"
 serde_json = "1.0"
+
+[lints.rust]
+unexpected_cfgs = { level = "warn", check-cfg = ['cfg(nightly)'] }