regression: in mysql/mariadb we are not using the defaultGTIDSet anymore.

[sravotto]

ERROR [Jul 28 09:17:00] error from replication source; continuing detail="missing gtidset\ngithub.com/cockroachdb/cdc-sink/internal/source/mylogical.(*conn).ReadInto\n\t/Users/sravotto/go/src/github.com/cockroachdb/cdc-sink/internal/source/mylogical/conn.go:198\ngithub.com/cockroachdb/cdc-sink/internal/source/logical.(*loop).runOnce.func1\n\t/Users/sravotto/go/src/github.com/cockroachdb/cdc-sink/internal/source/logical/loop.go:200\ngolang.org/x/sync/errgroup.(*Group).Go.func1\n\t/Users/sravotto/go/pkg/mod/golang.org/x/sync@v0.0.0-20220601150217-0de741cfad7f/errgroup/errgroup.go:75\nruntime.goexit\n\t/usr/local/opt/go/libexec/src/runtime/asm_amd64.s:1581" error="missing gtidset"

[sravotto]

Fixed with PR #196