lst: fix LineStatusTrackerManagerTest

Ensure that we dispatch `FileStatusManager.fileStatusesChanged` events before putting AfterUpdateRunnable request.
Otherwise, we might wait till the end of update, but accidentally trigger another one,
and `releaseUnneededTrackers` would do nothing.

Tests were blinking after 0ec7ee057a.

platform/vcs-impl/src/com/intellij/openapi/vcs/impl/LineStatusTrackerManager.kt

@@ -1025,6 +1025,10 @@ class LineStatusTrackerManager(
 
   @TestOnly
   fun waitUntilBaseContentsLoaded() {
+    if (ApplicationManager.getApplication().isDispatchThread) {
+      UIUtil.dispatchAllInvocationEvents()
+    }
+
     val semaphore = Semaphore()
     semaphore.down()