Add test for updating pk with duplicate

Author: ggilder

localtests/panic-on-warnings-update-pk-with-duplicate-on-new-unique-index/create.sql

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+drop table if exists gh_ost_test;
+create table gh_ost_test (
+  id int auto_increment,
+  email varchar(100) not null,
+  primary key (id)
+) auto_increment=1;
+
+insert into gh_ost_test (email) values ('alice@example.com');
+insert into gh_ost_test (email) values ('bob@example.com');
+insert into gh_ost_test (email) values ('charlie@example.com');
+
+drop event if exists gh_ost_test;
+delimiter ;;
+create event gh_ost_test
+  on schedule every 1 second
+  starts current_timestamp + interval 3 second
+  ends current_timestamp + interval 60 second
+  on completion not preserve
+  enable
+  do
+begin
+  -- This UPDATE modifies the primary key, so it will be converted to DELETE + INSERT
+  -- The INSERT will attempt to insert email='alice@example.com' (duplicate)
+  -- which violates the new unique index being added by the migration
+  -- Delay ensures this fires during binlog apply phase, not bulk copy
+  update gh_ost_test set id=10, email='alice@example.com' where id=2;
+end ;;

localtests/panic-on-warnings-update-pk-with-duplicate-on-new-unique-index/expect_failure

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+Warnings detected during DML event application

localtests/panic-on-warnings-update-pk-with-duplicate-on-new-unique-index/extra_args

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+--panic-on-warnings --alter "ADD UNIQUE KEY email_unique (email)"