Merge #97086

97086: kvserver: deflake test merge queue r=andrewbaptist a=kvoli

Previously, it was possible for ranges to spuriously merge when not expected to in `TestMergeQueue`. Unexpected merging occurred due to the merge delay interval being shorter than the time between test statements
- so that a merge could sneak when it shouldn't have. This was only realistically possible running `--stress` and with a slower `deadlock` build.

This commit updates the merge delay to be 1000 seconds, to avoid this situation occurring.

Informs: #97000

Release note: None

Co-authored-by: Austen McClernon <austen@cockroachlabs.com>

pkg/kv/kvserver/client_merge_test.go

@@ -4367,9 +4367,13 @@ func TestMergeQueue(t *testing.T) {
 		// NB: It is possible for the ranges being checked to record load
 		// during the test. To avoid flakiness, we set the splitByLoadStat high
 		// enough that any recorded load from testing won't exceed it.
+		// Likewise, when running under race - it is possible that if
+		// splitByLoadMergeDelay is small, enough time will pass in the test
+		// that this delay is elapsed and the ranges will merge when not
+		// expected to.
 		const splitByLoadStat = 10e9
 		const mergeByLoadStat = splitByLoadStat / 2 // see conservativeLoadBasedSplitThreshold
-		const splitByLoadMergeDelay = 500 * time.Millisecond
+		const splitByLoadMergeDelay = 1000 * time.Second
 
 		setSplitObjective := func(dim kvserver.LBRebalancingObjective) {
 			kvserver.LoadBasedRebalancingObjective.Override(ctx, sv, int64(dim))