Allow unknown clippy lints so that lints added in nightly don't break CI

src/lib.rs

@@ -1,6 +1,7 @@
 //! # halo2
 
 #![cfg_attr(docsrs, feature(doc_cfg))]
+#![allow(unknown_lints)]
 #![allow(
     clippy::op_ref,
     clippy::assign_op_pattern,
@@ -8,7 +9,8 @@
     clippy::suspicious_arithmetic_impl,
     clippy::many_single_char_names,
     clippy::same_item_push,
-    clippy::upper_case_acronyms
+    clippy::upper_case_acronyms,
+    clippy::unknown_clippy_lints
 )]
 #![deny(broken_intra_doc_links)]
 #![deny(missing_debug_implementations)]