tests: fix goroutine leak related to state snapshot generation (#28974)

---------

Co-authored-by: Felix Lange <fjl@twurst.com>

core/state/snapshot/snapshot.go

@@ -258,6 +258,14 @@ func (t *Tree) Disable() {
 	for _, layer := range t.layers {
 		switch layer := layer.(type) {
 		case *diskLayer:
+
+			layer.lock.RLock()
+			generating := layer.genMarker != nil
+			layer.lock.RUnlock()
+			if !generating {
+				// Generator is already aborted or finished
+				break
+			}
 			// If the base layer is generating, abort it
 			if layer.genAbort != nil {
 				abort := make(chan *generatorStats)