test/unreservable: add test for blocked jobs overmatching

problem: we didn't have a test to reproduce the issue with blocked jobs
being constantly reconsidered

solution: with the new failed stats support, after the fix there should
be no more than 10 failures to match, 14 is somewhat deterministic for
this test if the issue comes back.

t/t4013-unreservable.sh

@@ -58,12 +58,42 @@ test_expect_success 'create 3 jobs with the same constraint, so two are unreserv
 		--progress --jps \
 		--flags=waitable \
 		--setattr=exec.test.run_duration=0.01s \
-		sleep 0.25
+		sleep 0.5
 '
 
 test_expect_success 'ensure all three succeeded' '
   flux job wait -av
 '
+test_expect_success 'drain a few nodes' '
+	flux resource drain 1-5 test with drained nodes
+'
+test_expect_success 'create a set of 2 inactive jobs' '
+	flux submit --cc=1-2 --quiet \
+	  -N 1 --exclusive \
+		--flags=waitable \
+		--requires="host:fake[4]" \
+		--progress --jps \
+		--setattr=exec.test.run_duration=0.01s \
+		hostname
+'
+test_expect_success 'create a set of 2 running jobs' '
+	time flux submit --progress --jps --quiet --cc=1-2 --wait-event=start -N1 \
+		--flags=waitable \
+		--requires=compute \
+		--setattr=exec.test.run_duration=0.01s \
+		hostname
+'
+test_expect_success 'undrain nodes' '
+	flux resource undrain 1-5
+'
+test_expect_success 'ensure all four succeeded' '
+  flux job wait -av
+'
+test_expect_success 'failed match requests should be 10, but 14 is bad' '
+	NJOBS_FAILED="$(rpc sched-fluxion-resource.stats-get | jq ".match.failed.njobs")" &&
+  echo njobs failed $NJOBS_FAILED &&
+  test $NJOBS_FAILED = 10
+'
 test_expect_success 'unload fluxion' '
 	flux module remove sched-fluxion-qmanager &&
 	flux module remove sched-fluxion-resource &&