Revert unexpected_cfgs from expect to allow

The unexpected_cfgs are not being triggered in Bazel builds because we
have not yet wired up `--check-cfg` in those targets.

Author: dtolnay

gen/build/src/lib.rs

@@ -45,7 +45,7 @@
 //! ```
 
 #![doc(html_root_url = "https://docs.rs/cxx-build/1.0.179")]
-#![cfg_attr(not(check_cfg), expect(unexpected_cfgs))]
+#![cfg_attr(not(check_cfg), allow(unexpected_cfgs))]
 #![allow(
     clippy::cast_sign_loss,
     clippy::default_trait_access,

gen/cmd/src/main.rs

@@ -1,4 +1,4 @@
-#![cfg_attr(not(check_cfg), expect(unexpected_cfgs))]
+#![cfg_attr(not(check_cfg), allow(unexpected_cfgs))]
 #![allow(
     clippy::cast_sign_loss,
     clippy::default_trait_access,

gen/lib/src/lib.rs

@@ -10,7 +10,7 @@
 #![doc(html_root_url = "https://docs.rs/cxx-gen/0.7.179")]
 #![deny(missing_docs)]
 #![expect(dead_code)]
-#![cfg_attr(not(check_cfg), expect(unexpected_cfgs))]
+#![cfg_attr(not(check_cfg), allow(unexpected_cfgs))]
 #![allow(
     clippy::cast_sign_loss,
     clippy::default_trait_access,