Fix the check-cfg workflow (#2676)

* Fix unused cfg attributes

* Fix check-cfg workflow

Author: pvdrz

.github/workflows/bindgen.yml

@@ -238,7 +238,7 @@ jobs:
           override: true
 
       - name: Check cfg
-        run: cargo check -Z unstable-options -Z check-cfg=features
+        run: cargo check -Z unstable-options -Z check-cfg
 
   test-book:
     runs-on: ubuntu-latest

bindgen/ir/item.rs

@@ -98,13 +98,13 @@ pub(crate) trait ItemAncestors {
     fn ancestors<'a>(&self, ctx: &'a BindgenContext) -> ItemAncestorsIter<'a>;
 }
 
-#[cfg(__testing_only_extra_assertions)]
+#[cfg(feature = "__testing_only_extra_assertions")]
 type DebugOnlyItemSet = ItemSet;
 
-#[cfg(not(__testing_only_extra_assertions))]
+#[cfg(not(feature = "__testing_only_extra_assertions"))]
 struct DebugOnlyItemSet;
 
-#[cfg(not(__testing_only_extra_assertions))]
+#[cfg(not(feature = "__testing_only_extra_assertions"))]
 impl DebugOnlyItemSet {
     fn new() -> Self {
         DebugOnlyItemSet