Add missing tests for `go/event/syslogger` (#15005) #335

Job	Run time
Build and push vitess/lite Docker images (latest)	3m 5s
Build and push vitess/lite Docker images (mysql57)	2m 51s
Build and push vitess/lite Docker images (mysql80)	3m 2s
Build and push vitess/lite Docker images (percona57)	3m 4s
Build and push vitess/lite Docker images (percona80)	3m 4s
	15m 6s

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