kvserver: fix test merge queue when grunning unsupported

`TestMergeQueue/load-based-merging/switch...below-threshold` asserts
that switching the split objective between CPU and QPS will not cause
range's to merge, even if their pre-switch load qualified them for
merging.

This test was broken when `grunning` was unsupported, as the objective
never actually switches to anything other than QPS.

Add a check for `grunning` support, and assert that a merge occurs if
unsupported.

Fixes: cockroachdb#106937
Epic: none
Release note: None

Author: kvoli

pkg/kv/kvserver/client_merge_test.go

@@ -55,6 +55,7 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/testutils/skip"
 	"github.com/cockroachdb/cockroach/pkg/testutils/testcluster"
 	"github.com/cockroachdb/cockroach/pkg/util/ctxgroup"
+	"github.com/cockroachdb/cockroach/pkg/util/grunning"
 	"github.com/cockroachdb/cockroach/pkg/util/hlc"
 	"github.com/cockroachdb/cockroach/pkg/util/leaktest"
 	"github.com/cockroachdb/cockroach/pkg/util/log"
@@ -4525,7 +4526,14 @@ func TestMergeQueue(t *testing.T) {
 
 					clearRange(t, lhsStartKey, rhsEndKey)
 					setSplitObjective(secondSplitObjective)
-					verifyUnmergedSoon(t, store, lhsStartKey, rhsStartKey)
+					if !grunning.Supported() {
+						// CPU isn't a supported split objective when grunning isn't
+						// supported. Switching the dimension will have no effect, as the
+						// objective gets overridden in such cases to always be QPS.
+						verifyMergedSoon(t, store, lhsStartKey, rhsStartKey)
+					} else {
+						verifyUnmergedSoon(t, store, lhsStartKey, rhsStartKey)
+					}
 				})
 			}
 		}