MDEV-34952 main.log_slow test failure on opensuse builder

The loose regex for the MDEV-34539 test ended up
matching the opensuse in the path in buildbot.

Adjust to more complete regex including space,
backtick and \n, which becomes much less common
as a path name.

Author: grooverdan

mysql-test/main/log_slow.test

@@ -213,7 +213,7 @@ set log_slow_filter=default;
 set timestamp=default;
 
 let SEARCH_FILE=`select @@slow_query_log_file`;
-let SEARCH_PATTERN=use.*2;
+let SEARCH_PATTERN= use \`a\n.*2;
 let SEARCH_OUTPUT=matches;
 source include/search_pattern_in_file.inc;