Normal tea has caffeine, which isn't great for dogs. If it's normal "black" tea, I would dilute it with more milk in his portion - he may just like it because you're drinking it, and because of the milk in it, if you put milk or cream in your tea. I'd just keep it pretty diluted (tea flavored water more than "tea") and not give him very much, and you should be okay in your little time of sharing.

All this not withstanding, my police-chief grandfather, being a good Swede, had coffee and a doughnut when he came home from work late at night. Butchie, the family bulldog, got some of his coffee poured into his dish, and "helped" him eat his doughnut, too, to no ill effect.