manifest-schema: Apply clippy to doctest

https://github.com/taiki-e/github-actions/commit/96af4dc51482b761c058fdc8ef3a80b44a18e51f

tools/manifest-schema/src/lib.rs

@@ -6,10 +6,12 @@ Structured access to the install-action manifests.
 
 #![doc(test(
     no_crate_inject,
-    attr(
-        deny(warnings, rust_2018_idioms, single_use_lifetimes),
-        allow(dead_code, unused_variables)
-    )
+    attr(allow(
+        dead_code,
+        unused_variables,
+        clippy::undocumented_unsafe_blocks,
+        clippy::unused_trait_names,
+    ))
 ))]
 #![warn(
     // Lints that may help when writing public library.