volume: fix ReadOnly match arm missed by the tuple-variant change

#11544 made VolumeError::ReadOnly carry the volume id; the batch-write
fallback in write_volume_needles still matched and built it as a unit
variant, breaking the build (E0532/E0308).

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seaweed-volume/src/storage/store.rs

@@ -761,7 +761,7 @@ impl Store {
             Err(e) => writes
                 .iter()
                 .map(|_| match e {
-                    VolumeError::ReadOnly => Err(VolumeError::ReadOnly),
+                    VolumeError::ReadOnly(_) => Err(VolumeError::ReadOnly(vid)),
                     _ => Err(VolumeError::NotFound),
                 })
                 .collect(),