Fix ec.rebuild failing on unrepairable volumes instead of skipping (#8632)

* Fix ec.rebuild failing on unrepairable volumes instead of skipping them

When an EC volume has fewer shards than DataShardsCount, ec.rebuild would
return an error and abort the entire operation. Now it logs a warning and
continues rebuilding the remaining volumes.

Fixes #8630

* Remove duplicate volume ID in unrepairable log message

---------

Co-authored-by: Copilot <copilot@github.com>

weed/shell/command_ec_rebuild.go

@@ -231,12 +231,7 @@ func (erb *ecRebuilder) rebuildEcVolumes(collection string) {
 			continue
 		}
 		if shardCount < erasure_coding.DataShardsCount {
-			// Capture variables for closure
-			vid := vid
-			shardCount := shardCount
-			erb.ewg.Add(func() error {
-				return fmt.Errorf("ec volume %d is unrepairable with %d shards", vid, shardCount)
-			})
+			erb.write("ec volume %d is unrepairable with %d shards (need %d), skipping\n", vid, shardCount, erasure_coding.DataShardsCount)
 			continue
 		}