MDEV-25456 MariaBackup logs "[ERROR]" on Invalid log block checksum

Fix is to changed message to be [WARNING] for backup

Author: vaintroub

storage/innobase/log/log0recv.cc

@@ -967,7 +967,8 @@ log_group_read_log_seg(
 			DBUG_EXECUTE_IF("log_checksum_mismatch", { cksum = crc + 1; });
 
 			if (crc != cksum) {
-				ib::error() << "Invalid log block checksum."
+				ib::error_or_warn(srv_operation == SRV_OPERATION_BACKUP)
+					    << "Invalid log block checksum."
 					    << " block: " << block_number
 					    << " checkpoint no: "
 					    << log_block_get_checkpoint_no(buf)