MDEV-20959: binlog.binlog_parallel_replication_marks_row fails in buildbot with wrong result

Problem:
=======
Test "binlog.binlog_parallel_replication_marks_row" fails sporadically due to
result length mismatch.

Analysis:
=========
Test generates a binary log and it looks for certain words within the binary
log file and prints them. For example word like "GTID,BEGIN,COMMIT ...".
Binary log output contains base64 encoded characters. Occasionally the encoded
characters match with the above words and results in test failure.

+XwoFWxMBAAAALgAAAGEDAAAAAB8AAAAAAAEABHRlc3QAAnQxAAIDAwACFGTIDQ==
+AAAAAAAAAAAEEwQADQgICAoKCgGTIDw9

Fix:
===
Improve the regular expression to match exact words.

mysql-test/include/binlog_parallel_replication_marks.test

@@ -79,7 +79,7 @@ while (<F>) {
   s/end_log_pos \d+/end_log_pos #/;
   s/table id \d+/table id #/;
   s/mapped to number \d+/mapped to number #/;
-  print if /GTID|BEGIN|COMMIT|Table_map|Write_rows|Update_rows|Delete_rows|generated by server|40005 TEMPORARY/;
+  print if /\b(GTID|BEGIN|COMMIT|Table_map|Write_rows|Update_rows|Delete_rows|generated by server|40005 TEMPORARY)\b/;
 }
 close F;
 EOF