Allow the unused_braces lint which is too eager

See rust-lang/rust#70717

Author: shepmaster

.cirrus.yml

@@ -1,6 +1,7 @@
 env:
-  RUSTFLAGS: -D warnings
-  RUSTDOCFLAGS: -D warnings
+  # unused-braces is due to https://github.com/rust-lang/rust/issues/70717
+  RUSTFLAGS: -D warnings -Aunused-braces
+  RUSTDOCFLAGS: -D warnings -Aunused-braces
 
 stable_test_task:
   name: "Rust Stable"