chore: explicitly relaxed clippy lint for runtime entry macro (#4030)

tokio-macros/src/entry.rs

@@ -325,11 +325,13 @@ fn parse_knobs(
     let brace_token = input.block.brace_token;
     input.block = syn::parse2(quote_spanned! {last_stmt_end_span=>
         {
+            let body = async #body;
+            #[allow(clippy::expect_used)]
             #rt
                 .enable_all()
                 .build()
                 .expect("Failed building the Runtime")
-                .block_on(async #body)
+                .block_on(body)
         }
     })
     .expect("Parsing failure");