No macro needed. Blocks Pyroblast from being cast until fireball has been cast.
Thank you to Vardex for creating the original retail masterpiece.
Limitation:
This WA will not work when clicking the spell directly on the bar. It will also not work with any mouse keybinds like scroll wheel or side buttons.
Alternative:
https://wago.io/S9KU37W4R : A similar WA that instead of blocking the spell, freezes your game until the cast is over to simulate queuing. It might be able to create a lower gap between spells and might be a bit better with higher latency but freezing your game even if it's for a fifth of a second can be annoying.