Don't broadcast Checkable#next_check updates made just not to check t…

…wice

The checker sorts Checkables by next_check while picking the next due one,
so we (already) have to advance next_check while starting a check.
But the second master doesn't need this info, as it's not responsible.

lib/icinga/checkable-check.cpp

@@ -563,11 +563,11 @@ void Checkable::ExecuteCheck()
 
 	SetLastCheckStarted(Utility::GetTime());
 
-	/* This calls SetNextCheck() which updates the CheckerComponent's idle/pending
+	/* This calls SetNextCheck() for a later update of the CheckerComponent's idle/pending
 	 * queues and ensures that checks are not fired multiple times. ProcessCheckResult()
 	 * is called too late. See #6421.
 	 */
-	UpdateNextCheck();
+	UpdateNextCheck(nullptr, true);
 
 	bool reachable = IsReachable();
 
@@ -636,7 +636,7 @@ void Checkable::ExecuteCheck()
 			 * a check result from the remote instance. The check will be re-scheduled
 			 * using the proper check interval once we've received a check result.
 			 */
-			SetNextCheck(Utility::GetTime() + GetCheckCommand()->GetTimeout() + 30);
+			SetNextCheck(Utility::GetTime() + GetCheckCommand()->GetTimeout() + 30, true);
 
 		/*
 		 * Let the user know that there was a problem with the check if