t1019: change order of job cancellations

Problem: Running t1019-mf-priority-info-fetch.t under valgrind causes
the third submitted job to enter an alloc event by the time the first
two are canceled, which we don't want for the purpose of the tests
because we are checking for certain cur_run_jobs and cur_active_jobs
values when we query the plugin's internal map.

Change the order of the job cancellations to cancel the last submitted
job first so that it never enters the alloc event while the first two
are in the process of being cancelled.

t/t1019-mf-priority-info-fetch.t

@@ -73,10 +73,10 @@ test_expect_success HAVE_JQ 'fetch plugin state and make sure that jobs are refl
 	jq -e ".mf_priority_map[0].banks[0].cur_active_jobs == 3" <query_2.json
 '
 
-test_expect_success 'cancel jobs' '
-	flux job cancel $jobid1 &&
+test_expect_success 'cancel jobs in reverse order so last job does not get alloc event' '
+	flux job cancel $jobid3 &&
 	flux job cancel $jobid2 &&
-	flux job cancel $jobid3
+	flux job cancel $jobid1
 '
 
 test_expect_success 'add another user to flux-accounting DB and send it to plugin' '