FrogReaver
The most respectful and polite poster ever
Sure, and if this was the intent, then the feat would make no reference to the Attack action. It would simply say "you can take a bonus action to shove someone with your shield" or words to that effect. That would be a bonus action with no timing requirement/restriction, and thus you'd be free to do that bonus action any time you like. Given the fact that the feat does not use this wording, then it's clear that this is not how the feat is supposed to work.
That would allow it to be used with the cast a spell action. So the attack action mention is required in the feat.