s3: make SetModTime work for GLACIER while syncing - Fixes #3224

Before this change rclone would fail with

    Failed to set modification time: InvalidObjectState: Operation is not valid for the source object's storage class

when attempting to set the modification time of an object in GLACIER.

After this change rclone will re-upload the object as part of a sync if it needs to change the modification time.

See: https://forum.rclone.org/t/suspected-bug-in-s3-or-compatible-sync-logic-to-glacier/10187

backend/s3/s3.go

@@ -1736,6 +1736,9 @@ func (o *Object) SetModTime(modTime time.Time) error {
 	if o.fs.opt.SSEKMSKeyID != "" {
 		req.SSEKMSKeyId = &o.fs.opt.SSEKMSKeyID
 	}
+	if o.fs.opt.StorageClass == "GLACIER" || o.fs.opt.StorageClass == "DEEP_ARCHIVE" {
+		return fs.ErrorCantSetModTime
+	}
 	if o.fs.opt.StorageClass != "" {
 		req.StorageClass = &o.fs.opt.StorageClass
 	}