#You have not taken your action so the spellcasting is disrupted
Xanathar's Guide to Everything provides a rule that clarifies when casting a concentration spell ends concentration:
As soon as you start casting a spell or using a special ability that requires concentration, your concentration on another effect ends instantly. (XGE, 5)
This makes it clear that as soon as you start to cast another concentration spell Haste is ended
The question then remains whether you have already taken your action by beginning to cast the spell or whether you have only taken your action once you finish casting the spell. This question can be phrased as "When do I take my action?"
This is not exactly clear in the rules because it is rarely an issue. Most of the time you just take the action and that is that. There is reason to believe that RAI you have taken your action once you complete your action.
To begin the Sage Advice Compendium says that the Shield Master feat cannot be used to make a bonus action shove before the attack action has been taken. You can choose when to take Bonus Actions so long as the trigger has been satisfied so if you "take the attack action" as soon as you decide to do so then you would be able to "Take the Attack action --> Use your bonus action to shove --> make an attack --> possibly make an extra attack" which would be functionally equivalent to using the bonus action before taking the Attack action. Since using a bonus action is not allowed before taking the Attack Action we can conclude that you do not take the action as soon as you decide to do so.
There is additional support for this in Jeremy Crawford, one of the game designer's, unofficial tweets:
You can interrupt a multiple-attack action with a bonus action/reaction only if the trigger of the bonus action/reaction is an attack, rather than the action
- This was later clarified with regards to bonus actions without triggers but it does show that Jeremy Crawford at least believes that you have not "taken the Attack Action" until it is completed.
This is further supported (and contradicted) in a later tweet:
The simple by-the-book way (RAW) to determine whether you've completed an action is to finish the whole action.
Yet you fulfill our design intent (RAI) with the Attack action if you make at least one attack with it, since that is how we define the action in its basic form.
We are concerned with whether you have "taken" the action not whether you have "completed" the action but since Shield Master says "take the Attack Action" we can conclude that completing the action is equivalent to taking the action.
However the tweet also says that they intended for a single attack to satisfy the bonus action trigger. I think we can disregard this in the case of your question because there is not an equivalent form for casting a spell. Casting the spell is its most basic form.
###Summary Basically if you "take an action" as soon as you begin the action then you could use the Shield Master feat before making an attack. The designers clarified that you cannot do so and so we can therefore conclude that starting an action is not the same as taking the action.
Since Haste prevents you from taking an action until the end of your next turn and you have not yet "taken" the cast a spell action you therefore cannot cast another concentration spell on a turn where you are affected by Haste