Bug #30594 rpl.rpl_skip_error is nondeterministic

Non-determinism in the tests was due to results of SBR are different from those gained
with row binlog format.

Because tests effectively verify skipping only ER_DUP_ENTRY it is explicitly required
to run the test on in mixed and stmt binlog format.
ER_DUP_ENTRY is automatically ignored when happened in RBR because of implicit rule
favoring reentrant reading from binlog rule
which means that a Write_rows_log_event overwrites a slave's row
if the one has the same primary key.

If future we might have skipping error due to applying of row-based events.
The comments added saying a new file would be needed for that: rpl_row_skip_error or smth.

mysql-test/suite/rpl/t/rpl_skip_error.test

@@ -3,6 +3,14 @@
 #########################################
 # Note that errors are ignored by opt file.
 source include/master-slave.inc;
+source include/have_binlog_format_mixed_or_statement.inc;
+
+#
+# Bug #30594
+# Skipping error due to applying Row-based repliation events
+# should be checked with another test file
+# consider names like rpl_row_skip_error
+#
 
 create table t1 (n int not null primary key);
 save_master_pos;