Fix flaky testUnattributedSession_afterAllNotificationsPastAttributionWindow test

This test failed about half the time due to not waiting for some
background threads. Ensured this test now passes with the Xcode run
repeatly with 100 times.

Author: jkasten2

iOS_SDK/OneSignalSDK/UnitTests/OutcomeIntegrationTests.m

@@ -347,15 +347,18 @@ - (void)testUnattributedSession_afterAllNotificationsPastAttributionWindow {
 
     // 2. Close the app for 31 seconds
     [UnitTestCommonMethods backgroundApp];
+    [UnitTestCommonMethods runBackgroundThreads];
     [NSDateOverrider advanceSystemTimeBy:31];
 
     // 3. Receive 1 notification in background
     [UnitTestCommonMethods receiveNotification:@"test_notification_1" wasOpened:NO];
+    [UnitTestCommonMethods runBackgroundThreads];
 
     // 4. Open app
-    [UnitTestCommonMethods initOneSignal_andThreadWaitWithForeground];
+    [UnitTestCommonMethods foregroundApp];
+    [UnitTestCommonMethods runBackgroundThreads];
 
-    // 5. Make sure NOTIFICATION influence is DIRECT and has 1 notification
+    // 5. Make sure NOTIFICATION influence is INDIRECT and has 1 notification
     NSArray<OSInfluence *> *sessionInfluences = [[OSSessionManager sharedSessionManager] getInfluences];
     for (OSInfluence *influence in sessionInfluences) {
         switch (influence.influenceChannel) {
@@ -375,6 +378,7 @@ - (void)testUnattributedSession_afterAllNotificationsPastAttributionWindow {
 
     // 7. Open app
     [UnitTestCommonMethods foregroundApp];
+    [UnitTestCommonMethods runBackgroundThreads];
 
     // 8. Make sure all influences are UNATTRIBUTED and has 0 notifications
     sessionInfluences = [[OSSessionManager sharedSessionManager] getInfluences];