Relax lock when updating job history information

In #6767 we introduced the ability to track job execution history, but
looks like we exaggerated the lock level when marking the end of the job
execution using `ShareRowExclusiveLock` that conflicts with autovacuum
jobs that requires an `ShareUpdateExclusiveLock`, so relaxing the lock
to `RowExclusiveLock` because we only update the tuple in the job
execution history metadata table.

src/bgw/job_stat_history.c

@@ -270,7 +270,7 @@ ts_bgw_job_stat_history_mark_end(BgwJob *job, JobResult result, Jsonb *edata)
 										  bgw_job_stat_history_tuple_mark_end,
 										  NULL,
 										  &context,
-										  ShareRowExclusiveLock))
+										  RowExclusiveLock))
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 					 errmsg("unable to find job history " INT64_FORMAT, new_job->job_history.id)));