MDEV-11700 funcs_2.innodb_charset fails in buldbot on valgrind builder with timeout

When the test is run as a part of the suite with valgrind,
only allow it to be executed if --big-test is set.
If the test is run by specifying its name explicitly, it
will still be executed, even with valgrind without big-test,
MTR has special logic for that

Author: elenst

mysql-test/suite/funcs_2/t/innodb_charset.test

@@ -6,6 +6,7 @@
 # Checking of other prerequisites is in charset_master.test                    #
 ################################################################################
 
+--source include/no_valgrind_without_big.inc
 --source include/have_innodb.inc
 
 let $engine_type= InnoDB;