message: Improve unpin() checks
diff: @@ -740,10 +740,10 @@ mod tests {
  assert_eq!(cache.stats().misses, 0);
  // unpin again has no effect
  - let _ = cache.unpin_wasm(&id);
  + let _ = cache.unpin_wasm(&id).unwrap();
  // unpin non existent id has no effect
  let non_id = Checksum::generate(b"non_existent");
  - let _ = cache.unpin_wasm(&non_id);
  + let _ = cache.unpin_wasm(&non_id).unwrap();
  }
  }
  