fixup(#6991): it broke the macOS build (#7024)

pageserver/src/virtual_file/io_engine.rs

@@ -248,6 +248,7 @@ impl IoEngine {
                 .await
                 .expect("failed to join blocking code most likely it panicked, panicking as well")
             }
+            #[cfg(target_os = "linux")]
             IoEngine::TokioEpollUring => work.await,
         }
     }