don't resume task for unsupported collation error

dm/worker/task_checker.go

@@ -263,19 +263,19 @@ func isResumableError(err *pb.ProcessError) bool {
 	case pb.ErrorType_ExecSQL:
 		// not elegant code, because TiDB doesn't expose some error
 		for _, msg := range retry.UnsupportedDDLMsgs {
-			if err.Error != nil && strings.Contains(err.Error.RawCause, msg) {
+			if err.Error != nil && strings.Contains(strings.ToLower(err.Error.RawCause), strings.ToLower(msg)) {
 				return false
 			}
 		}
 		for _, msg := range retry.UnsupportedDMLMsgs {
-			if err.Error != nil && strings.Contains(err.Error.RawCause, msg) {
+			if err.Error != nil && strings.Contains(strings.ToLower(err.Error.RawCause), strings.ToLower(msg)) {
 				return false
 			}
 		}
 	case pb.ErrorType_UnknownError:
 		if err.Error != nil && err.Error.ErrCode == int32(terror.ErrParserParseRelayLog.Code()) {
 			for _, msg := range retry.ParseRelayLogErrMsgs {
-				if strings.Contains(err.Error.Message, msg) {
+				if strings.Contains(strings.ToLower(err.Error.Message), strings.ToLower(msg)) {
 					return false
 				}
 			}

pkg/retry/errors.go

@@ -27,6 +27,7 @@ var (
 		"unsupported modify charset",
 		"unsupported modify collate",
 		"unsupported drop integer primary key",
+		"Unsupported collation",
 	}
 
 	// UnsupportedDMLMsgs list the error messages of some un-recoverable DML, which is used in task auto recovery